apex-test-class

Apex Test Class Skill

Core Principles

1. Bulkify tests - Always test with 200+ records to catch governor limit issues
2. Isolate test data - Use @TestSetup and TestDataFactory; never rely on org data
3. Assert meaningfully - Test behavior, not just coverage; include failure messages
4. Mock external dependencies - Use HttpCalloutMock, Test.setMock() for integrations
5. Test negative paths - Validate error handling, not just happy paths

Test Class Structure

@IsTest
private class MyServiceTest {

@TestSetup
static void setupTestData() {
    // Create shared test data using TestDataFactory
    List<Account> accounts = TestDataFactory.createAccounts(200, true);
}

@IsTest
static void shouldPerformExpectedBehavior_WhenValidInput() {
    // Given: Setup specific test state
    List<Account> accounts = [SELECT Id, Name FROM Account];
    
    // When: Execute the code under test
    Test.startTest();
    MyService.processAccounts(accounts);
    Test.stopTest();
    
    // Then: Assert expected outcomes
    List<Account> updated = [SELECT Id, Status__c FROM Account];
    System.Assert.areEqual(200, updated.size(), 'All accounts should be processed');
    for (Account acc : updated) {
        System.Assert.areEqual('Processed', acc.Status__c, 'Status should be updated');
    }
}

@IsTest
static void shouldThrowException_WhenInvalidInput() {
    // Given
    List<Account> emptyList = new List<Account>();
    
    // When/Then
    Test.startTest();
    try {
        MyService.processAccounts(emptyList);
        System.Assert.fail('Expected MyCustomException to be thrown');
    } catch (MyCustomException e) {
        System.Assert.isTrue(e.getMessage().contains('cannot be empty'), 
            'Exception message should indicate empty input');
    }
    Test.stopTest();
}

}

## Naming Convention

Use descriptive method names: `should[ExpectedBehavior]_When[Condition]`

Examples:
- `shouldCreateContact_WhenAccountIsActive`
- `shouldThrowException_WhenEmailIsInvalid`
- `shouldSendNotification_WhenOpportunityClosedWon`
- `shouldBypassTrigger_WhenRunningAsBatch`

## Test.startTest() / Test.stopTest()

Always wrap the code under test:
- Resets governor limits for accurate limit testing
- Executes async operations synchronously (queueables, batch, future)
- Fires scheduled jobs immediately

## Reference Files

Detailed patterns for specific scenarios:

- **[references/test-data-factory.md](references/test-data-factory.md)** - TestDataFactory class patterns and field defaults
- **[references/assertion-patterns.md](references/assertion-patterns.md)** - Assertion best practices and common pitfalls
- **[references/mocking-patterns.md](references/mocking-patterns.md)** - HttpCalloutMock, Test.setMock(), stubbing
- **[references/async-testing.md](references/async-testing.md)** - Batch, Queueable, Future, Scheduled job testing

## Quick Reference: What to Test

| Component | Key Test Scenarios |
|-----------|-------------------|
| Trigger | Bulk insert/update/delete, recursion, field changes |
| Service | Valid/invalid inputs, bulk operations, exceptions |
| Controller | Page load, action methods, view state |
| Batch | Start/execute/finish, chunking, error records |
| Queueable | Chaining, bulkification, error handling |
| Callout | Success response, error response, timeout |
| Scheduled | Execution, CRON validation |