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, runn

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: 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 Test Method Structure Use Given/When/Then: Negative Test — Exception Pattern Use try/catch with Assert.fail to verify expected exceptions: 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. 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 when class metadata crosses from versions 66.0 and below to 67.0 and above, check explicit sharing, decide user/system mode per operation, grant required CRUD/FLS in test users or permission sets, and rerun affected tests 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 platform apex generate 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](references/test data factory.md) TestDataFactory patterns, field overrides, duplicate rule handling [references/assertion patterns.md](references/assertion patterns.md) Assertion best practices, anti patterns, common pitfalls [references/mocking patterns.md](references/mocking patterns.md) HttpCalloutMock, DML mocking, StubProvider, SOSL, Email, Platform Events [references/async testing.md](references/async testing.md) Batch, Queueable, Future, Scheduled job testing

platform-apex-test-generate