generating-apex-test

What this skill does

# Generating Apex Tests

Generate production-ready Apex test classes and run disciplined test-fix loops with coverage analysis.

## Core Principles

1. **One behavior per method** — each test method validates a single scenario. Separate positive, negative, and bulk tests. NEVER combine related-but-distinct inputs (e.g., null and empty) in one method — create `_NullInput_` and `_EmptyInput_` as separate test methods
2. **Bulkify tests** — test with 251+ records to cross the 200-record trigger batch boundary. **Batch Apex exception:** in test context only one `execute()` invocation runs, so set `batchSize >= testRecordCount`. See [references/async-testing.md](references/async-testing.md)
3. **Isolate test data** — every `@TestSetup` must delegate record creation to a `TestDataFactory` class. If none exists, create one first. Never build record lists inline in `@TestSetup`. Never rely on org data (`SeeAllData=false`) or hardcoded IDs. For duplicate rule handling, see [references/test-data-factory.md](references/test-data-factory.md)
4. **Assert meaningfully** — use exact expected values computed from test data setup. NEVER use range assertions or approximate counts when the value is deterministic. Always include failure messages. See [references/assertion-patterns.md](references/assertion-patterns.md)
5. **Use `Assert` class only** — `Assert.areEqual`, `Assert.isTrue`, `Assert.fail`, etc. Never use legacy `System.assert`, `System.assertEquals`, or `System.assertNotEquals`
6. **Mock external boundaries** — use `HttpCalloutMock` for callouts, `Test.setFixedSearchResults` for SOSL, DML mock classes for database isolation. Design for testability via constructor injection. See [references/mocking-patterns.md](references/mocking-patterns.md)
7. **Test negative paths** — validate error handling and exception scenarios, not just happy paths
8. **Wrap with start/stop** — pair `Test.startTest()` with `Test.stopTest()` to reset governor limits and force async execution

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

Always wrap the code under test in `Test.startTest()` / `Test.stopTest()`:

- Resets governor limits so the test measures only the code under test
- Executes async operations synchronously (queueables, batch, future methods)
- Fires scheduled jobs immediately

## Test Code Anti-Patterns

| Anti-Pattern | Fix |
|---|---|
| SOQL/DML inside loops | Query once before the loop; use `Map<Id, SObject>` for lookups |
| Magic numbers in assertions | Derive expected values from setup constants |
| God test class (>500 lines) | Split into multiple test classes by behavior area |
| Long test methods (>30 lines) | Extract Given/When/Then into helper methods |
| Generic `Exception` catch | Catch the specific expected type (e.g., `DmlException`) |

## Workflow

### Step 1 — Gather Context

Before generating or fixing tests, identify:

- the target production class(es) under test
- existing test classes, test data factories, and setup helpers
- desired test scope (single class, specific methods, suite, or local tests)
- coverage threshold (75% minimum for deploy, 90%+ recommended)
- org alias when running tests against an org

### Step 2 — Generate the Test Class

Apply the structure, naming conventions, and patterns from the asset templates and reference docs.

**MANDATORY — File Deliverables:** For every test class, create BOTH files:
1. `{ClassName}Test.cls` — the test class (use [assets/test-class-template.cls](assets/test-class-template.cls) as starting point)
2. `{ClassName}Test.cls-meta.xml` — the metadata file:

```xml
<?xml version="1.0" encoding="UTF-8"?>
<ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>66.0</apiVersion>
    <status>Active</status>
</ApexClass>
```

If no `TestDataFactory` exists in the project, create `TestDataFactory.cls` + `TestDataFactory.cls-meta.xml` using [assets/test-data-factory-template.cls](assets/test-data-factory-template.cls).

#### @TestSetup Example

```apex
@TestSetup
static void setupTestData() {
    List<Account> accounts = TestDataFactory.createAccounts(251, true);
}
```

#### Test Method Structure

Use Given/When/Then:

```apex
@isTest
static void shouldUpdateStatus_WhenValidInput() {
    // Given
    List<Account> accounts = [SELECT Id FROM Account];

    // When
    Test.startTest();
    MyService.processAccounts(accounts);
    Test.stopTest();

    // Then
    List<Account> updated = [SELECT Id, Status__c FROM Account];
    Assert.areEqual(251, updated.size(), 'All accounts should be processed');
}
```

#### Negative Test — Exception Pattern

Use try/catch with `Assert.fail` to verify expected exceptions:

```apex
@isTest
static void shouldThrowException_WhenInvalidInput() {
    // Given
    List<Account> emptyList = new List<Account>();

    // When/Then
    Test.startTest();
    try {
        MyService.processAccounts(emptyList);
        Assert.fail('Expected MyCustomException to be thrown');
    } catch (MyCustomException e) {
        Assert.isTrue(e.getMessage().contains('cannot be empty'),
            'Exception message should indicate empty input');
    }
    Test.stopTest();
}
```

#### Naming Convention

- `should[ExpectedResult]_When[Scenario]`: `shouldSendNotification_WhenOpportunityClosedWon`
- `[SubjectOrAction]_[Scenario]_[ExpectedResult]`: `AccountUpdate_ChangeName_Success`

### Step 3 — Run Tests

Start narrow when debugging; widen after the fix is stable.

```bash
# Single test class
sf apex run test --class-names MyServiceTest --result-format human --code-coverage --target-org <alias>

# Specific test methods
sf apex run test --tests MyServiceTest.shouldUpdateStatus_WhenValidInput --result-format human --target-org <alias>

# All local tests
sf apex run test --test-level RunLocalTests --result-format human --code-coverage --target-org <alias>
```

### Step 4 — Analyze Results

Focus on:

- failing methods — exception types and stack traces
- uncovered lines and weak coverage areas
- whether failures indicate bad test data, brittle assertions, or broken production logic

### Step 5 — Fix Loop

When tests fail, run a disciplined fix loop (max 3 iterations — stop and surface root cause if still failing):

1. Read the failing test class and the class under test
2. Identify root cause from error messages and stack traces
3. Apply fix — adjust test data or assertions for test-side issues; delegate production code issues to the `generating-apex` skill
4. Rerun the focused test before broader regression
5. Repeat until all tests pass, iteration limit reached, or root cause requires design change

### Step 6 — Validate Coverage

| Level | Coverage | Purpose |
|-------|----------|---------|
| Production deploy | 75% minimum | Required by Salesforce |
| Recommended | 90%+ | Best practice target |
| Critical paths | 100% | Business-critical code |

Cover all paths: positive, negative/exception, bulk (251+ records), callout/async.

## What to Test by Component

| Component | Key Test Scenarios |
|-----------|-------------------|
| Trigger | Bulk insert/update/delete, recursion guard, field change detection |
| Service | Valid/invalid inputs, bulk operations, exception handling |
| Controller | Page load, action methods, view state |
| Batch | start/execute/finish, scope matching (batch size >= record count), `Database.Stateful` tracking, error handling, chaining (separate methods — `finish()` calling `Database.executeBatch()` throws `UnexpectedException`) |
| Queueable | Chaining (only first job runs in tests), bulkification, error handling, callout mocks before `Test.startTest()` |
| Callout | Success response, error response, timeout |
| Selector | Valid/null/empty inputs, bulk (251+), field population, sort order, `WITH USER_MODE` via `System.runAs` |
| Scheduled | Direct execution via `execute(null)`, CRON registration via `CronTrigger` query |
| Platform Event | `Test.enableChangeDataCapture()`, `Test.getEventBus().deliver()`, verify subscriber side effects |

## Output Expectations

Del