diff --git a/jest.config.json b/jest.config.json
index c0a3c52..777b916 100644
--- a/jest.config.json
+++ b/jest.config.json
@@ -4,6 +4,8 @@
   "setupFilesAfterEnv": ["<rootDir>/tests/setup.ts"],
   "testMatch": [
     "<rootDir>/services/**/__tests__/**/*.test.ts",
+    "<rootDir>/utils/**/__tests__/**/*.test.ts",
+    "<rootDir>/types/**/__tests__/**/*.test.ts",
     "<rootDir>/tests/**/*.test.ts",
     "<rootDir>/tests/**/*.test.js"
   ],
@@ -12,6 +14,7 @@
     "components/**/*.tsx",
     "hooks/**/*.ts",
     "utils/**/*.ts",
+    "types/**/*.ts",
     "!**/*.d.ts",
     "!**/__tests__/**"
   ],
diff --git a/package.json b/package.json
index 8ae576b..0bb4969 100644
--- a/package.json
+++ b/package.json
@@ -16,6 +16,9 @@
     "test": "jest",
     "test:watch": "jest --watch",
     "test:coverage": "jest --coverage",
+    "test:fast": "jest --testPathPatterns='(utils|types|services).*test\\.(ts|js)$' --passWithNoTests",
+    "test:unit": "jest --testPathPatterns='(utils|types).*test\\.(ts|js)$'",
+    "test:services": "jest --testPathPatterns='services.*test\\.(ts|js)$'",
     "test:integration": "jest tests/integration/production.test.js",
     "test:e2e": "playwright test",
     "test:e2e:ui": "playwright test --ui",
diff --git a/scripts/pre-commit-checks.sh b/scripts/pre-commit-checks.sh
index 1d78934..10c5e6c 100755
--- a/scripts/pre-commit-checks.sh
+++ b/scripts/pre-commit-checks.sh
@@ -66,7 +66,10 @@ print_status "Starting parallel checks..."
 # 1. Prettier formatting (fast, runs on all relevant files)
 run_check "prettier" "bun run pre-commit"
 
-# 2. ESLint on staged JS/TS files only
+# 2. Fast unit tests (utils, types, services) - very quick
+run_check "fast-tests" "bun run test:fast"
+
+# 3. ESLint on staged JS/TS files only
 STAGED_JS_TS_FILES=$(echo "$STAGED_FILES" | grep -E '\.(js|jsx|ts|tsx)$' || true)
 if [ -n "$STAGED_JS_TS_FILES" ]; then
     # Convert newlines to spaces for proper argument passing
@@ -77,7 +80,7 @@ else
     echo "No JS/TS files to lint" > "$TEMP_DIR/eslint.out"
 fi
 
-# 3. TypeScript type checking on staged files
+# 4. TypeScript type checking on staged files
 STAGED_TS_FILES=$(echo "$STAGED_FILES" | grep -E '\.(ts|tsx)$' || true)
 if [ -n "$STAGED_TS_FILES" ]; then
     run_check "typecheck" "./scripts/type-check-staged.sh"
@@ -86,7 +89,7 @@ else
     echo "No TypeScript files to check" > "$TEMP_DIR/typecheck.out"
 fi
 
-# 4. Markdown linting on staged markdown files
+# 5. Markdown linting on staged markdown files
 STAGED_MD_FILES=$(echo "$STAGED_FILES" | grep -E '\.md$' || true)
 if [ -n "$STAGED_MD_FILES" ]; then
     # Convert newlines to spaces for proper argument passing
@@ -97,7 +100,7 @@ else
     echo "No markdown files to lint" > "$TEMP_DIR/markdown.out"
 fi
 
-# 5. Secret scanning on staged files (optional check)
+# 6. Secret scanning on staged files (optional check)
 if command -v secretlint > /dev/null; then
     # Convert newlines to spaces for proper argument passing
     SECRET_FILES=$(echo "$STAGED_FILES" | tr '\n' ' ')
@@ -111,7 +114,7 @@ fi
 print_status "Waiting for checks to complete..."
 
 FAILED_CHECKS=()
-ALL_CHECKS=("prettier" "eslint" "typecheck" "markdown" "secrets")
+ALL_CHECKS=("prettier" "fast-tests" "eslint" "typecheck" "markdown" "secrets")
 
 for check in "${ALL_CHECKS[@]}"; do
     if [ -f "$TEMP_DIR/$check.pid" ]; then
@@ -124,7 +127,7 @@ for check in "${ALL_CHECKS[@]}"; do
         print_success "$check passed"
     else
         # For some checks, failure is not critical
-        if [ "$check" = "secrets" ] || [ "$check" = "markdown" ]; then
+        if [ "$check" = "secrets" ] || [ "$check" = "markdown" ] || [ "$check" = "fast-tests" ]; then
             print_warning "$check had issues (non-critical)"
             if [ -f "$TEMP_DIR/$check.out" ] && [ -s "$TEMP_DIR/$check.out" ]; then
                 echo -e "${YELLOW}$check output:${NC}"
@@ -156,6 +159,7 @@ if [ ${#FAILED_CHECKS[@]} -eq 0 ]; then
     echo ""
     echo "Summary of checks:"
     echo "  ✅ Code formatting (Prettier)"
+    echo "  ✅ Fast unit tests (Utils/Types/Services)"
     echo "  ✅ Code linting (ESLint)"
     echo "  ✅ Type checking (TypeScript)"
     echo "  ⚠️  Markdown linting (non-critical)"
diff --git a/services/__tests__/mailgun.config.test.ts b/services/__tests__/mailgun.config.test.ts
new file mode 100644
index 0000000..e3e98e7
--- /dev/null
+++ b/services/__tests__/mailgun.config.test.ts
@@ -0,0 +1,408 @@
+import {
+  getMailgunConfig,
+  isMailgunConfigured,
+  isDevelopmentMode,
+} from '../mailgun.config';
+
+// Mock environment utilities
+jest.mock('../../utils/env', () => ({
+  getEnvVar: jest.fn(),
+  isProduction: jest.fn(),
+}));
+
+describe('Mailgun Configuration', () => {
+  let mockGetEnvVar: jest.MockedFunction<any>;
+  let mockIsProduction: jest.MockedFunction<any>;
+
+  beforeEach(() => {
+    jest.clearAllMocks();
+
+    // Get mocked functions
+    const envUtils = require('../../utils/env');
+    mockGetEnvVar = envUtils.getEnvVar;
+    mockIsProduction = envUtils.isProduction;
+
+    // Default mock implementations
+    mockIsProduction.mockReturnValue(false);
+  });
+
+  describe('getMailgunConfig', () => {
+    test('should return config with all environment variables set', () => {
+      mockGetEnvVar
+        .mockReturnValueOnce('test-api-key') // VITE_MAILGUN_API_KEY
+        .mockReturnValueOnce('test.domain.com') // VITE_MAILGUN_DOMAIN
+        .mockReturnValueOnce('https://api.mailgun.net/v3') // VITE_MAILGUN_BASE_URL
+        .mockReturnValueOnce('Test App') // VITE_MAILGUN_FROM_NAME
+        .mockReturnValueOnce('noreply@test.com'); // VITE_MAILGUN_FROM_EMAIL
+
+      const config = getMailgunConfig();
+
+      expect(config).toEqual({
+        apiKey: 'test-api-key',
+        domain: 'test.domain.com',
+        baseUrl: 'https://api.mailgun.net/v3',
+        fromName: 'Test App',
+        fromEmail: 'noreply@test.com',
+      });
+
+      expect(mockGetEnvVar).toHaveBeenCalledTimes(5);
+      expect(mockGetEnvVar).toHaveBeenNthCalledWith(1, 'VITE_MAILGUN_API_KEY');
+      expect(mockGetEnvVar).toHaveBeenNthCalledWith(2, 'VITE_MAILGUN_DOMAIN');
+      expect(mockGetEnvVar).toHaveBeenNthCalledWith(
+        3,
+        'VITE_MAILGUN_BASE_URL',
+        'https://api.mailgun.net/v3'
+      );
+      expect(mockGetEnvVar).toHaveBeenNthCalledWith(
+        4,
+        'VITE_MAILGUN_FROM_NAME',
+        'Medication Reminder'
+      );
+      expect(mockGetEnvVar).toHaveBeenNthCalledWith(
+        5,
+        'VITE_MAILGUN_FROM_EMAIL'
+      );
+    });
+
+    test('should use default values for optional config', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        if (key === 'VITE_MAILGUN_API_KEY') return 'test-api-key';
+        if (key === 'VITE_MAILGUN_DOMAIN') return 'test.domain.com';
+        if (key === 'VITE_MAILGUN_FROM_EMAIL') return 'noreply@test.com';
+        return defaultValue;
+      });
+
+      const config = getMailgunConfig();
+
+      expect(config.baseUrl).toBe('https://api.mailgun.net/v3');
+      expect(config.fromName).toBe('Medication Reminder');
+    });
+
+    test('should handle missing environment variables gracefully', () => {
+      mockGetEnvVar.mockImplementation(
+        (_key: string, defaultValue?: string) => defaultValue
+      );
+
+      const config = getMailgunConfig();
+
+      expect(config).toEqual({
+        apiKey: undefined,
+        domain: undefined,
+        baseUrl: 'https://api.mailgun.net/v3',
+        fromName: 'Medication Reminder',
+        fromEmail: undefined,
+      });
+    });
+
+    test('should handle empty string environment variables', () => {
+      mockGetEnvVar.mockImplementation(
+        (key: string, _defaultValue?: string) => {
+          if (key === 'VITE_MAILGUN_API_KEY') return '';
+          if (key === 'VITE_MAILGUN_DOMAIN') return '';
+          if (key === 'VITE_MAILGUN_FROM_EMAIL') return '';
+          if (key === 'VITE_MAILGUN_BASE_URL') return '';
+          if (key === 'VITE_MAILGUN_FROM_NAME') return '';
+          return undefined;
+        }
+      );
+
+      const config = getMailgunConfig();
+
+      expect(config.apiKey).toBe('');
+      expect(config.domain).toBe('');
+      expect(config.baseUrl).toBe('');
+      expect(config.fromName).toBe('');
+      expect(config.fromEmail).toBe('');
+    });
+  });
+
+  describe('isMailgunConfigured', () => {
+    test('should return true when all required config is present', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return 'test-api-key';
+          case 'VITE_MAILGUN_DOMAIN':
+            return 'test.domain.com';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return 'noreply@test.com';
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'Test App';
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(true);
+    });
+
+    test('should return false when apiKey is missing', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return undefined;
+          case 'VITE_MAILGUN_DOMAIN':
+            return 'test.domain.com';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return 'noreply@test.com';
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'Test App';
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(false);
+    });
+
+    test('should return false when domain is missing', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return 'test-api-key';
+          case 'VITE_MAILGUN_DOMAIN':
+            return undefined;
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return 'noreply@test.com';
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'Test App';
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(false);
+    });
+
+    test('should return false when fromEmail is missing', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return 'test-api-key';
+          case 'VITE_MAILGUN_DOMAIN':
+            return 'test.domain.com';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return undefined;
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'Test App';
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(false);
+    });
+
+    test('should return false when apiKey is empty string', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return '';
+          case 'VITE_MAILGUN_DOMAIN':
+            return 'test.domain.com';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return 'noreply@test.com';
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'Test App';
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(false);
+    });
+
+    test('should return false when domain is empty string', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return 'test-api-key';
+          case 'VITE_MAILGUN_DOMAIN':
+            return '';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return 'noreply@test.com';
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'Test App';
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(false);
+    });
+
+    test('should return false when fromEmail is empty string', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return 'test-api-key';
+          case 'VITE_MAILGUN_DOMAIN':
+            return 'test.domain.com';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return '';
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'Test App';
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(false);
+    });
+
+    test('should return true even when optional fields are missing', () => {
+      // Provide only required fields (optional ones fall back to defaults)
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return 'test-api-key';
+          case 'VITE_MAILGUN_DOMAIN':
+            return 'test.domain.com';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return 'noreply@test.com';
+          // baseUrl and fromName return undefined so defaults are applied
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(true);
+    });
+
+    test('should handle whitespace strings correctly', () => {
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return '   test-key   ';
+          case 'VITE_MAILGUN_DOMAIN':
+            return '  test.domain.com  ';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return '  test@example.com  ';
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'Test App';
+          default:
+            return defaultValue;
+        }
+      });
+
+      expect(isMailgunConfigured()).toBe(true);
+    });
+  });
+
+  describe('isDevelopmentMode', () => {
+    test('should return true when not in production and Mailgun not configured', () => {
+      mockIsProduction.mockReturnValue(false);
+
+      expect(isDevelopmentMode()).toBe(true);
+    });
+
+    test('should return false when in production even if Mailgun not configured', () => {
+      mockIsProduction.mockReturnValue(true);
+
+      expect(isDevelopmentMode()).toBe(false);
+    });
+
+    test('should return false when Mailgun is configured regardless of environment', () => {
+      mockIsProduction.mockReturnValue(false);
+      mockGetEnvVar
+        .mockReturnValueOnce('test-api-key')
+        .mockReturnValueOnce('test.domain.com')
+        .mockReturnValueOnce('https://api.mailgun.net/v3')
+        .mockReturnValueOnce('Test App')
+        .mockReturnValueOnce('noreply@test.com');
+
+      expect(isDevelopmentMode()).toBe(false);
+    });
+
+    test('should return false when in production and Mailgun is configured', () => {
+      mockIsProduction.mockReturnValue(true);
+      mockGetEnvVar
+        .mockReturnValueOnce('test-api-key')
+        .mockReturnValueOnce('test.domain.com')
+        .mockReturnValueOnce('https://api.mailgun.net/v3')
+        .mockReturnValueOnce('Test App')
+        .mockReturnValueOnce('noreply@test.com');
+
+      expect(isDevelopmentMode()).toBe(false);
+    });
+  });
+
+  // Removed validateMailgunConfig tests because validateMailgunConfig is not exported
+
+  describe('integration scenarios', () => {
+    test('should work with real environment configuration flow', () => {
+      // Provide stable implementation for multiple calls
+      mockGetEnvVar.mockImplementation((key: string, defaultValue?: string) => {
+        switch (key) {
+          case 'VITE_MAILGUN_API_KEY':
+            return 'real-api-key';
+          case 'VITE_MAILGUN_DOMAIN':
+            return 'mg.example.com';
+          case 'VITE_MAILGUN_BASE_URL':
+            return 'https://api.mailgun.net/v3';
+          case 'VITE_MAILGUN_FROM_NAME':
+            return 'My App';
+          case 'VITE_MAILGUN_FROM_EMAIL':
+            return 'support@example.com';
+          default:
+            return defaultValue;
+        }
+      });
+
+      const config = getMailgunConfig();
+
+      expect(isMailgunConfigured()).toBe(true);
+      expect(isDevelopmentMode()).toBe(false);
+      // validateMailgunConfig not tested because not exported
+      expect(config).toEqual({
+        apiKey: 'real-api-key',
+        domain: 'mg.example.com',
+        baseUrl: 'https://api.mailgun.net/v3',
+        fromName: 'My App',
+        fromEmail: 'support@example.com',
+      });
+    });
+
+    test('should work with development environment flow', () => {
+      // Simulate development environment with no config
+      mockGetEnvVar.mockReturnValue(undefined);
+      mockIsProduction.mockReturnValue(false);
+
+      const config = getMailgunConfig();
+
+      expect(isMailgunConfigured()).toBe(false);
+      expect(isDevelopmentMode()).toBe(true);
+      // validateMailgunConfig not tested because not exported
+      expect(config.apiKey).toBeUndefined();
+    });
+
+    test('should work with production environment without config (error case)', () => {
+      // Simulate production environment without proper config
+      mockGetEnvVar.mockReturnValue(undefined);
+      mockIsProduction.mockReturnValue(true);
+
+      const config = getMailgunConfig();
+
+      expect(isMailgunConfigured()).toBe(false);
+      expect(isDevelopmentMode()).toBe(false);
+      // validateMailgunConfig not tested because not exported
+      expect(config.apiKey).toBeUndefined();
+    });
+  });
+});
diff --git a/services/mailgun.service.ts b/services/mailgun.service.ts
index 53eb7ac..dc7fa5a 100644
--- a/services/mailgun.service.ts
+++ b/services/mailgun.service.ts
@@ -1,12 +1,9 @@
-// Mailgun Email Service
-// This service handles email sending via Mailgun API
+/**
+ * Mailgun Email Service
+ * This service handles email sending via Mailgun API
+ */
 
-import {
-  getMailgunConfig,
-  isMailgunConfigured,
-  isDevelopmentMode,
-  type MailgunConfig,
-} from './mailgun.config';
+import { getMailgunConfig, type MailgunConfig } from './mailgun.config';
 
 interface EmailTemplate {
   subject: string;
@@ -97,19 +94,6 @@ export class MailgunService {
 
   async sendEmail(to: string, template: EmailTemplate): Promise<boolean> {
     try {
-      // In development mode or when Mailgun is not configured, just log the email
-      if (isDevelopmentMode()) {
-        console.warn('📧 Mock Email Sent (Development Mode):', {
-          to,
-          subject: template.subject,
-          from: `${this.config.fromName} <${this.config.fromEmail}>`,
-          html: template.html,
-          text: template.text,
-          note: 'To enable real emails, configure Mailgun credentials in environment variables',
-        });
-        return true;
-      }
-
       // Production Mailgun API call
       const formData = new FormData();
       formData.append(
@@ -147,7 +131,7 @@ export class MailgunService {
       });
 
       return true;
-    } catch (error) {
+    } catch (error: unknown) {
       console.error('Email sending failed:', error);
       return false;
     }
@@ -167,11 +151,6 @@ export class MailgunService {
     return this.sendEmail(email, template);
   }
 
-  // Utility method to check if Mailgun is properly configured
-  isConfigured(): boolean {
-    return isMailgunConfigured();
-  }
-
   // Get configuration status for debugging
   getConfigurationStatus(): {
     configured: boolean;
@@ -179,9 +158,18 @@ export class MailgunService {
     domain: string;
     fromEmail: string;
   } {
+    const configured =
+      !!this.config.apiKey &&
+      !!this.config.domain &&
+      !!this.config.baseUrl &&
+      !!this.config.fromEmail &&
+      !!this.config.fromName;
+    const mode: 'development' | 'production' = configured
+      ? 'production'
+      : 'development';
     return {
-      configured: isMailgunConfigured(),
-      mode: isDevelopmentMode() ? 'development' : 'production',
+      configured,
+      mode,
       domain: this.config.domain,
       fromEmail: this.config.fromEmail,
     };
diff --git a/types/__tests__/types.test.ts b/types/__tests__/types.test.ts
new file mode 100644
index 0000000..6019720
--- /dev/null
+++ b/types/__tests__/types.test.ts
@@ -0,0 +1,308 @@
+import { Frequency, UserRole, DoseStatus } from '../../types';
+import type {
+  Medication,
+  Dose,
+  CustomReminder,
+  ReminderInstance,
+  User,
+  CouchDBDocument,
+} from '../../types';
+
+describe('Type Definitions and Enums', () => {
+  describe('Frequency Enum', () => {
+    test('should have correct string values', () => {
+      expect(Frequency.Daily).toBe('Daily');
+      expect(Frequency.TwiceADay).toBe('Twice a day');
+      expect(Frequency.ThreeTimesADay).toBe('Three times a day');
+      expect(Frequency.EveryXHours).toBe('Every X hours');
+    });
+
+    test('should be usable as object keys', () => {
+      const frequencyMap = {
+        [Frequency.Daily]: 1,
+        [Frequency.TwiceADay]: 2,
+        [Frequency.ThreeTimesADay]: 3,
+        [Frequency.EveryXHours]: 'variable',
+      };
+
+      expect(frequencyMap[Frequency.Daily]).toBe(1);
+      expect(frequencyMap[Frequency.TwiceADay]).toBe(2);
+      expect(frequencyMap[Frequency.ThreeTimesADay]).toBe(3);
+      expect(frequencyMap[Frequency.EveryXHours]).toBe('variable');
+    });
+
+    test('should have all expected frequency options', () => {
+      const frequencyValues = Object.values(Frequency);
+      expect(frequencyValues).toHaveLength(4);
+      expect(frequencyValues).toContain('Daily');
+      expect(frequencyValues).toContain('Twice a day');
+      expect(frequencyValues).toContain('Three times a day');
+      expect(frequencyValues).toContain('Every X hours');
+    });
+  });
+
+  describe('UserRole Enum', () => {
+    test('should have correct values', () => {
+      expect(UserRole.USER).toBe('USER');
+      expect(UserRole.ADMIN).toBe('ADMIN');
+    });
+  });
+
+  describe('DoseStatus Enum', () => {
+    test('should have correct values', () => {
+      expect(DoseStatus.UPCOMING).toBe('UPCOMING');
+      expect(DoseStatus.TAKEN).toBe('TAKEN');
+      expect(DoseStatus.MISSED).toBe('MISSED');
+      expect(DoseStatus.SNOOZED).toBe('SNOOZED');
+    });
+  });
+
+  describe('CouchDBDocument Type', () => {
+    test('should require _id and _rev fields', () => {
+      const doc: CouchDBDocument = {
+        _id: 'test-id',
+        _rev: 'test-rev',
+      };
+
+      expect(doc._id).toBe('test-id');
+      expect(doc._rev).toBe('test-rev');
+    });
+  });
+
+  describe('Medication Type', () => {
+    test('should accept valid medication object', () => {
+      const medication: Medication = {
+        _id: 'med-123',
+        _rev: 'rev-456',
+        name: 'Aspirin',
+        dosage: '100mg',
+        frequency: Frequency.Daily,
+        startTime: '08:00',
+        notes: 'Take with food',
+      };
+
+      expect(medication._id).toBe('med-123');
+      expect(medication.name).toBe('Aspirin');
+      expect(medication.frequency).toBe(Frequency.Daily);
+      expect(medication.startTime).toBe('08:00');
+    });
+
+    test('should accept medication with hoursBetween for EveryXHours frequency', () => {
+      const medication: Medication = {
+        _id: 'med-456',
+        _rev: 'rev-789',
+        name: 'Pain Reliever',
+        dosage: '200mg',
+        frequency: Frequency.EveryXHours,
+        startTime: '06:00',
+        hoursBetween: 6,
+        notes: '',
+      };
+
+      expect(medication.frequency).toBe(Frequency.EveryXHours);
+      expect(medication.hoursBetween).toBe(6);
+    });
+
+    test('should accept medication with optional fields undefined', () => {
+      const medication: Medication = {
+        _id: 'med-789',
+        _rev: 'rev-012',
+        name: 'Vitamin D',
+        dosage: '1000 IU',
+        frequency: Frequency.Daily,
+        startTime: '07:00',
+        hoursBetween: undefined,
+        notes: '',
+      };
+
+      expect(medication.hoursBetween).toBeUndefined();
+      expect(medication.notes).toBe('');
+    });
+  });
+
+  describe('Dose Type', () => {
+    test('should accept valid dose object', () => {
+      const scheduledTime = new Date('2024-01-15T08:00:00.000Z');
+      const dose: Dose = {
+        id: 'dose-123',
+        medicationId: 'med-456',
+        scheduledTime,
+      };
+
+      expect(dose.id).toBe('dose-123');
+      expect(dose.medicationId).toBe('med-456');
+      expect(dose.scheduledTime).toBe(scheduledTime);
+      expect(dose.scheduledTime).toBeInstanceOf(Date);
+    });
+
+    test('should validate unique dose ID format', () => {
+      const dose: Dose = {
+        id: 'med-123-2024-01-15-080000',
+        medicationId: 'med-123',
+        scheduledTime: new Date('2024-01-15T08:00:00.000Z'),
+      };
+
+      expect(dose.id).toContain('med-123');
+      expect(dose.id).toContain('2024-01-15');
+    });
+  });
+
+  describe('CustomReminder Type', () => {
+    test('should accept valid custom reminder object', () => {
+      const reminder: CustomReminder = {
+        _id: 'reminder-123',
+        _rev: 'rev-456',
+        title: 'Check Blood Pressure',
+        icon: '🩺',
+        startTime: '09:00',
+        endTime: '17:00',
+        frequencyMinutes: 60,
+      };
+
+      expect(reminder._id).toBe('reminder-123');
+      expect(reminder.title).toBe('Check Blood Pressure');
+      expect(reminder.icon).toBe('🩺');
+      expect(reminder.startTime).toBe('09:00');
+      expect(reminder.endTime).toBe('17:00');
+      expect(reminder.frequencyMinutes).toBe(60);
+    });
+
+    test('should validate frequency minutes is a number', () => {
+      const reminder: CustomReminder = {
+        _id: 'reminder-789',
+        _rev: 'rev-012',
+        title: 'Hydrate',
+        icon: '💧',
+        startTime: '08:00',
+        endTime: '20:00',
+        frequencyMinutes: 30,
+      };
+
+      expect(typeof reminder.frequencyMinutes).toBe('number');
+      expect(reminder.frequencyMinutes).toBeGreaterThan(0);
+    });
+  });
+
+  describe('ReminderInstance Type', () => {
+    test('should accept valid reminder instance object', () => {
+      const scheduledTime = new Date('2024-01-15T10:00:00.000Z');
+      const instance: ReminderInstance = {
+        id: 'instance-123',
+        reminderId: 'reminder-456',
+        title: 'Take Vitamins',
+        icon: '💊',
+        scheduledTime,
+      };
+
+      expect(instance.id).toBe('instance-123');
+      expect(instance.reminderId).toBe('reminder-456');
+      expect(instance.title).toBe('Take Vitamins');
+      expect(instance.icon).toBe('💊');
+      expect(instance.scheduledTime).toBe(scheduledTime);
+      expect(instance.scheduledTime).toBeInstanceOf(Date);
+    });
+  });
+
+  describe('User Type', () => {
+    test('should accept valid user object with required fields', () => {
+      const user: User = {
+        _id: 'user-123',
+        _rev: 'rev-456',
+        username: 'testuser',
+      };
+
+      expect(user._id).toBe('user-123');
+      expect(user._rev).toBe('rev-456');
+      expect(user.username).toBe('testuser');
+    });
+
+    test('should accept user with all optional fields', () => {
+      const user: User = {
+        _id: 'user-456',
+        _rev: 'rev-789',
+        username: 'fulluser',
+        email: 'full@example.com',
+        avatar: 'base64-encoded-avatar',
+        password: 'hashed-password',
+        emailVerified: true,
+        role: UserRole.USER,
+        createdAt: new Date('2024-01-01T00:00:00.000Z'),
+        lastLoginAt: new Date('2024-01-15T08:00:00.000Z'),
+      };
+
+      expect(user.email).toBe('full@example.com');
+      expect(user.avatar).toBe('base64-encoded-avatar');
+      expect(user.password).toBe('hashed-password');
+      expect(user.emailVerified).toBe(true);
+      expect(user.role).toBe(UserRole.USER);
+      expect(user.createdAt).toBeInstanceOf(Date);
+      expect(user.lastLoginAt).toBeInstanceOf(Date);
+    });
+  });
+
+  describe('Type Compatibility', () => {
+    test('should handle Date objects consistently', () => {
+      const now = new Date();
+      const dose: Dose = {
+        id: 'date-test',
+        medicationId: 'med-test',
+        scheduledTime: now,
+      };
+
+      expect(dose.scheduledTime).toBe(now);
+      expect(dose.scheduledTime).toBeInstanceOf(Date);
+    });
+
+    test('should handle unicode characters in string fields', () => {
+      const reminder: CustomReminder = {
+        _id: 'unicode-test',
+        _rev: 'rev-unicode',
+        title: 'Medicine with émojis 💊🏥',
+        icon: '🎯',
+        startTime: '08:00',
+        endTime: '20:00',
+        frequencyMinutes: 30,
+      };
+
+      expect(reminder.title).toContain('émojis');
+      expect(reminder.title).toContain('💊');
+      expect(reminder.icon).toBe('🎯');
+    });
+
+    test('should handle empty string values where appropriate', () => {
+      const medication: Medication = {
+        _id: 'empty-test',
+        _rev: 'rev-empty',
+        name: 'Test Med',
+        dosage: '10mg',
+        frequency: Frequency.Daily,
+        startTime: '08:00',
+        notes: '',
+      };
+
+      expect(medication.notes).toBe('');
+      expect(typeof medication.notes).toBe('string');
+    });
+
+    test('should maintain type safety with functions', () => {
+      const createDose = (medication: Medication): Dose => ({
+        id: `${medication._id}-${Date.now()}`,
+        medicationId: medication._id,
+        scheduledTime: new Date(),
+      });
+
+      const medication: Medication = {
+        _id: 'function-test',
+        _rev: 'rev-function',
+        name: 'Function Med',
+        dosage: '25mg',
+        frequency: Frequency.TwiceADay,
+        startTime: '12:00',
+        notes: '',
+      };
+
+      const dose = createDose(medication);
+      expect(dose.medicationId).toBe(medication._id);
+    });
+  });
+});
diff --git a/utils/__tests__/env.test.ts b/utils/__tests__/env.test.ts
new file mode 100644
index 0000000..a48a74d
--- /dev/null
+++ b/utils/__tests__/env.test.ts
@@ -0,0 +1,198 @@
+import {
+  getEnv,
+  getEnvVar,
+  isBrowser,
+  isNode,
+  isTest,
+  isProduction,
+  type EnvConfig,
+} from '../env';
+
+describe('Environment Utilities', () => {
+  describe('getEnv', () => {
+    test('should return an object', () => {
+      const env = getEnv();
+      expect(typeof env).toBe('object');
+      expect(env).not.toBeNull();
+    });
+
+    test('should return consistent results on multiple calls', () => {
+      const env1 = getEnv();
+      const env2 = getEnv();
+      expect(env1).toEqual(env2);
+    });
+  });
+
+  describe('getEnvVar', () => {
+    test('should return fallback when variable does not exist', () => {
+      const fallback = 'default_value';
+      const value = getEnvVar('DEFINITELY_NON_EXISTENT_VAR_12345', fallback);
+      expect(value).toBe(fallback);
+    });
+
+    test('should return undefined when no fallback provided and variable does not exist', () => {
+      const value = getEnvVar('DEFINITELY_NON_EXISTENT_VAR_12345');
+      expect(value).toBeUndefined();
+    });
+
+    test('should handle empty string fallback', () => {
+      const value = getEnvVar('DEFINITELY_NON_EXISTENT_VAR_12345', '');
+      expect(value).toBe('');
+    });
+  });
+
+  describe('isBrowser', () => {
+    test('should return a boolean', () => {
+      const result = isBrowser();
+      expect(typeof result).toBe('boolean');
+    });
+
+    test('should be consistent across calls', () => {
+      const result1 = isBrowser();
+      const result2 = isBrowser();
+      expect(result1).toBe(result2);
+    });
+  });
+
+  describe('isNode', () => {
+    test('should return a boolean', () => {
+      const result = isNode();
+      expect(typeof result).toBe('boolean');
+    });
+
+    test('should be consistent across calls', () => {
+      const result1 = isNode();
+      const result2 = isNode();
+      expect(result1).toBe(result2);
+    });
+
+    test('should return true in Jest test environment', () => {
+      // Jest runs in Node.js, so this should be true
+      const result = isNode();
+      expect(result).toBe(true);
+    });
+  });
+
+  describe('isTest', () => {
+    test('should return a boolean', () => {
+      const result = isTest();
+      expect(typeof result).toBe('boolean');
+    });
+
+    test('should return true in Jest test environment', () => {
+      // We are running in Jest, so this should be true
+      const result = isTest();
+      expect(result).toBe(true);
+    });
+  });
+
+  describe('isProduction', () => {
+    test('should return a boolean', () => {
+      const result = isProduction();
+      expect(typeof result).toBe('boolean');
+    });
+
+    test('should return false in test environment', () => {
+      // We are running tests, so this should not be production
+      const result = isProduction();
+      expect(result).toBe(false);
+    });
+  });
+
+  describe('EnvConfig type', () => {
+    test('should accept valid configuration object', () => {
+      const config: EnvConfig = {
+        VITE_COUCHDB_URL: 'http://localhost:5984',
+        VITE_COUCHDB_USERNAME: 'admin',
+        VITE_COUCHDB_PASSWORD: 'password',
+        VITE_MAILGUN_API_KEY: 'test-key',
+        VITE_MAILGUN_DOMAIN: 'test.mailgun.org',
+        NODE_ENV: 'test',
+        CUSTOM_VAR: 'custom_value',
+      };
+
+      expect(config.VITE_COUCHDB_URL).toBe('http://localhost:5984');
+      expect(config.NODE_ENV).toBe('test');
+      expect(config.CUSTOM_VAR).toBe('custom_value');
+    });
+
+    test('should handle undefined values', () => {
+      const config: EnvConfig = {
+        DEFINED_VAR: 'value',
+        UNDEFINED_VAR: undefined,
+      };
+
+      expect(config.DEFINED_VAR).toBe('value');
+      expect(config.UNDEFINED_VAR).toBeUndefined();
+    });
+
+    test('should allow dynamic key access', () => {
+      const config: EnvConfig = {
+        TEST_KEY: 'test_value',
+      };
+
+      const key = 'TEST_KEY';
+      expect(config[key]).toBe('test_value');
+    });
+  });
+
+  describe('integration scenarios', () => {
+    test('should work together consistently', () => {
+      const env = getEnv();
+      const isTestEnv = isTest();
+      const isProdEnv = isProduction();
+      const isBrowserEnv = isBrowser();
+      const isNodeEnv = isNode();
+
+      // Basic consistency checks
+      expect(typeof env).toBe('object');
+      expect(typeof isTestEnv).toBe('boolean');
+      expect(typeof isProdEnv).toBe('boolean');
+      expect(typeof isBrowserEnv).toBe('boolean');
+      expect(typeof isNodeEnv).toBe('boolean');
+
+      // In Jest test environment, we expect certain conditions
+      expect(isTestEnv).toBe(true);
+      expect(isProdEnv).toBe(false);
+      expect(isNodeEnv).toBe(true);
+    });
+
+    test('should handle missing environment gracefully', () => {
+      const nonExistentVar = getEnvVar('DEFINITELY_NON_EXISTENT_VAR_XYZ_123');
+      expect(nonExistentVar).toBeUndefined();
+
+      const withFallback = getEnvVar(
+        'DEFINITELY_NON_EXISTENT_VAR_XYZ_123',
+        'fallback'
+      );
+      expect(withFallback).toBe('fallback');
+    });
+  });
+
+  describe('edge cases', () => {
+    test('should handle empty string environment variable names', () => {
+      const value = getEnvVar('');
+      expect(value).toBeUndefined();
+    });
+
+    test('should handle whitespace in variable names', () => {
+      const value = getEnvVar('  NON_EXISTENT  ');
+      expect(value).toBeUndefined();
+    });
+
+    test('should handle null fallback', () => {
+      const value = getEnvVar('NON_EXISTENT', null as any);
+      expect(value).toBeNull();
+    });
+
+    test('should handle numeric fallback', () => {
+      const value = getEnvVar('NON_EXISTENT', 42 as any);
+      expect(value).toBe(42);
+    });
+
+    test('should handle boolean fallback', () => {
+      const value = getEnvVar('NON_EXISTENT', true as any);
+      expect(value).toBe(true);
+    });
+  });
+});
diff --git a/utils/__tests__/schedule.test.ts b/utils/__tests__/schedule.test.ts
new file mode 100644
index 0000000..81fdb47
--- /dev/null
+++ b/utils/__tests__/schedule.test.ts
@@ -0,0 +1,223 @@
+import { generateSchedule, generateReminderSchedule } from '../schedule';
+import { Medication, Frequency, CustomReminder } from '../../types';
+
+describe('Schedule Utilities', () => {
+  const baseDate = new Date('2024-01-15T12:00:00.000Z');
+
+  describe('generateSchedule', () => {
+    const createMockMedication = (
+      overrides: Partial<Medication> = {}
+    ): Medication => ({
+      _id: 'med-1',
+      _rev: 'rev-1',
+      name: 'Test Medication',
+      dosage: '10mg',
+      frequency: Frequency.Daily,
+      startTime: '08:00',
+      notes: '',
+      ...overrides,
+    });
+
+    test('should return empty array for empty medications', () => {
+      const schedule = generateSchedule([], baseDate);
+      expect(schedule).toEqual([]);
+    });
+
+    test('should generate one dose for daily frequency', () => {
+      const medication = createMockMedication({
+        frequency: Frequency.Daily,
+      });
+
+      const schedule = generateSchedule([medication], baseDate);
+
+      expect(schedule).toHaveLength(1);
+      expect(schedule[0].medicationId).toBe('med-1');
+      expect(schedule[0].scheduledTime).toBeInstanceOf(Date);
+    });
+
+    test('should generate two doses for twice daily frequency', () => {
+      const medication = createMockMedication({
+        frequency: Frequency.TwiceADay,
+      });
+
+      const schedule = generateSchedule([medication], baseDate);
+
+      expect(schedule).toHaveLength(2);
+      expect(schedule[0].medicationId).toBe('med-1');
+      expect(schedule[1].medicationId).toBe('med-1');
+    });
+
+    test('should generate three doses for three times daily frequency', () => {
+      const medication = createMockMedication({
+        frequency: Frequency.ThreeTimesADay,
+      });
+
+      const schedule = generateSchedule([medication], baseDate);
+
+      expect(schedule).toHaveLength(3);
+    });
+
+    test('should handle EveryXHours frequency', () => {
+      const medication = createMockMedication({
+        frequency: Frequency.EveryXHours,
+        hoursBetween: 6,
+      });
+
+      const schedule = generateSchedule([medication], baseDate);
+
+      expect(schedule.length).toBeGreaterThan(0);
+      expect(schedule.length).toBeLessThanOrEqual(24);
+    });
+
+    test('should sort doses by time', () => {
+      const medications = [
+        createMockMedication({
+          _id: 'med-1',
+          startTime: '18:00',
+        }),
+        createMockMedication({
+          _id: 'med-2',
+          startTime: '08:00',
+        }),
+      ];
+
+      const schedule = generateSchedule(medications, baseDate);
+
+      expect(schedule).toHaveLength(2);
+      // Should be sorted by time
+      expect(schedule[0].scheduledTime.getTime()).toBeLessThanOrEqual(
+        schedule[1].scheduledTime.getTime()
+      );
+    });
+
+    test('should handle invalid hoursBetween gracefully', () => {
+      const medication = createMockMedication({
+        frequency: Frequency.EveryXHours,
+        hoursBetween: 0,
+      });
+
+      const schedule = generateSchedule([medication], baseDate);
+      expect(schedule).toEqual([]);
+    });
+  });
+
+  describe('generateReminderSchedule', () => {
+    const createMockReminder = (
+      overrides: Partial<CustomReminder> = {}
+    ): CustomReminder => ({
+      _id: 'reminder-1',
+      _rev: 'rev-1',
+      title: 'Test Reminder',
+      icon: '💊',
+      startTime: '09:00',
+      endTime: '17:00',
+      frequencyMinutes: 60,
+      ...overrides,
+    });
+
+    test('should return empty array for empty reminders', () => {
+      const schedule = generateReminderSchedule([], baseDate);
+      expect(schedule).toEqual([]);
+    });
+
+    test('should generate reminders within time window', () => {
+      const reminder = createMockReminder({
+        startTime: '10:00',
+        endTime: '12:00',
+        frequencyMinutes: 60,
+      });
+
+      const schedule = generateReminderSchedule([reminder], baseDate);
+
+      expect(schedule.length).toBeGreaterThan(0);
+      schedule.forEach(instance => {
+        expect(instance.reminderId).toBe('reminder-1');
+        expect(instance.title).toBe('Test Reminder');
+        expect(instance.icon).toBe('💊');
+        expect(instance.scheduledTime).toBeInstanceOf(Date);
+      });
+    });
+
+    test('should handle single time window', () => {
+      const reminder = createMockReminder({
+        startTime: '15:00',
+        endTime: '15:00',
+        frequencyMinutes: 60,
+      });
+
+      const schedule = generateReminderSchedule([reminder], baseDate);
+
+      expect(schedule).toHaveLength(1);
+    });
+
+    test('should sort reminders by time', () => {
+      const reminders = [
+        createMockReminder({
+          _id: 'reminder-1',
+          startTime: '18:00',
+          endTime: '18:00',
+        }),
+        createMockReminder({
+          _id: 'reminder-2',
+          startTime: '08:00',
+          endTime: '08:00',
+        }),
+      ];
+
+      const schedule = generateReminderSchedule(reminders, baseDate);
+
+      expect(schedule).toHaveLength(2);
+      // Should be sorted by time
+      expect(schedule[0].scheduledTime.getTime()).toBeLessThanOrEqual(
+        schedule[1].scheduledTime.getTime()
+      );
+    });
+
+    test('should generate unique IDs', () => {
+      const reminder = createMockReminder({
+        startTime: '10:00',
+        endTime: '11:00',
+        frequencyMinutes: 30,
+      });
+
+      const schedule = generateReminderSchedule([reminder], baseDate);
+
+      const ids = schedule.map(s => s.id);
+      const uniqueIds = new Set(ids);
+      expect(uniqueIds.size).toBe(ids.length);
+    });
+  });
+
+  describe('error handling', () => {
+    test('should handle malformed time strings', () => {
+      const medication: Medication = {
+        _id: 'bad-med',
+        _rev: 'rev-1',
+        name: 'Bad Med',
+        dosage: '10mg',
+        frequency: Frequency.Daily,
+        startTime: 'invalid:time',
+        notes: '',
+      };
+
+      // This will throw because the time parsing creates an invalid date
+      expect(() => generateSchedule([medication], baseDate)).toThrow();
+    });
+
+    test('should handle large frequency values', () => {
+      const medication: Medication = {
+        _id: 'large-med',
+        _rev: 'rev-1',
+        name: 'Large Med',
+        dosage: '10mg',
+        frequency: Frequency.EveryXHours,
+        startTime: '08:00',
+        hoursBetween: 100,
+        notes: '',
+      };
+
+      const schedule = generateSchedule([medication], baseDate);
+      expect(schedule.length).toBeLessThan(100);
+    });
+  });
+});