generating-apex-test

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name: generating-apex-test description: "Generate and validate Apex test classes with TestDataFactory patterns, bulk testing (251+ records), mocking strategies, assertion best practices, and disciplined test-fix loops. Use this skill when creating new Apex test classes, improving test coverage, debugging and fixing failing Apex tests, running test execution and coverage analysis, or implementing testing patterns for triggers, services, controllers, batch jobs, queueables, and integrations. Triggers on *Test.cls, *_Test.cls files, sf apex run test workflows, coverage reports, test-fix loops. Do NOT trigger for production Apex code (use generating-apex) or Jest/LWC tests." metadata: version: "1.0"

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
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
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
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
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 as starting point)
2. {ClassName}Test.cls-meta.xml — the metadata file:

<?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.

@TestSetup Example

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

Test Method Structure

Use Given/When/Then:

@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:

@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.

# 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

Deliverables per test class:

• {ClassName}Test.cls + {ClassName}Test.cls-meta.xml (match API version of class under test; default 66.0)
• TestDataFactory.cls + TestDataFactory.cls-meta.xml (if not already present)

Reference Files

Load on demand for detailed patterns:

Reference	When to use
references/test-data-factory.md	TestDataFactory patterns, field overrides, duplicate rule handling
references/assertion-patterns.md	Assertion best practices, anti-patterns, common pitfalls
references/mocking-patterns.md	HttpCalloutMock, DML mocking, StubProvider, SOSL, Email, Platform Events
references/async-testing.md	Batch, Queueable, Future, Scheduled job testing