Generating Apex Test

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

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

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

What to Test by Component

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:

Credits & Acknowledgments

This skill is built on established Salesforce Apex development patterns and the collective knowledge of the Salesforce developer community.

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Assertion Patterns

Assertion Methods

Always include the message parameter — makes test failures actionable.

Good vs Bad Assertions

Bad: No message, tests coverage not behavior

Assert.isTrue(result); // no message
Assert.isTrue(accounts.size() > 0); // vague — use areEqual with exact count

Good: Descriptive message, tests specific behavior

Assert.isTrue(result, 'Service should return true for valid input');
Assert.areEqual(200, accounts.size(), 'All 200 accounts should be processed');

Common Assertion Patterns

Collection Size

Assert.areEqual(200, results.size(), 'Should process all 200 records');
Assert.isTrue(results.isEmpty(), 'No results expected for invalid input');
Assert.isFalse(results.isEmpty(), 'Results should not be empty');

Field Values

Assert.areEqual('Processed', acc.Status__c, 'Account status should be updated to Processed');

for (Account acc : updatedAccounts) {
    Assert.areEqual('Active', acc.Status__c,
        'Account ' + acc.Name + ' should have Active status');
}

Exception Testing

@isTest
static void shouldThrowException_WhenInputInvalid() {
    Test.startTest();
    try {
        MyService.process(null);
        Assert.fail('Expected MyCustomException for null input');
    } catch (MyCustomException e) {
        Assert.isTrue(e.getMessage().contains('cannot be null'),
            'Exception message should mention null input');
    }
    Test.stopTest();
}

DML Results

// Insert success
Database.SaveResult[] results = Database.insert(accounts, false);
for (Database.SaveResult sr : results) {
    Assert.isTrue(sr.isSuccess(), 'Insert should succeed: ' + sr.getErrors());
}

Database.SaveResult sr = Database.insert(invalidAccount, false);
Assert.isFalse(sr.isSuccess(), 'Insert should fail for invalid data');
Assert.isTrue(sr.getErrors()[0].getMessage().contains('REQUIRED_FIELD_MISSING'),
    'Error should indicate missing required field');

Null Checks

Assert.isNull(result.ErrorMessage__c, 'No error expected for valid input');
Assert.isNotNull(result.Id, 'Record should have been inserted');

Date/DateTime

Assert.areEqual(Date.today(), record.CreatedDate__c, 'Should be created today');
Assert.isTrue(record.DueDate__c >= Date.today(), 'Due date should be in the future');

Anti-Patterns

Async Testing Patterns

Key Principle

Test.stopTest() forces all async operations to execute synchronously, allowing assertions on their results.

Batch Apex Testing

Basic Batch Test

Critical: In test context only one execute() invocation runs, so always set batchSize >= testRecordCount (e.g., Database.executeBatch(batch, 200) with 200 records). Never create more records than the batch size.

@isTest
static void shouldProcessAllRecords_WhenBatchExecutes() {
    List<Account> accounts = TestDataFactory.createAccounts(200, true);

    Test.startTest();
    MyBatchClass batch = new MyBatchClass();
    Id batchId = Database.executeBatch(batch, 200);
    Test.stopTest();

    List<Account> updated = [SELECT Id, Status__c FROM Account];
    for (Account acc : updated) {
        Assert.areEqual('Processed', acc.Status__c,
            'Batch should update all account statuses');
    }
}

Batch with Failures

@isTest
static void shouldLogErrors_WhenRecordsFail() {
    List<Account> accounts = TestDataFactory.createAccounts(198, true);

    List<Account> invalidAccounts = new List<Account>();
    for (Integer i = 0; i < 2; i++) {
        invalidAccounts.add(new Account(
            Name = 'Invalid Account ' + i,
            Invalid_Field__c = 'triggers_validation_error'
        ));
    }
    insert invalidAccounts;

    Test.startTest();
    MyBatchClass batch = new MyBatchClass();
    Database.executeBatch(batch, 200);
    Test.stopTest();

    List<Error_Log__c> errors = [SELECT Id, Message__c FROM Error_Log__c];
    Assert.areEqual(2, errors.size(), 'Should log 2 failed records');
}

Batch Chaining

Test finish() chaining in a separate test method — calling Database.executeBatch() inside finish() during a test can throw UnexpectedException. Verify the first batch independently, then test that finish() enqueues the next batch.

Queueable Testing

Basic Queueable Test

@isTest
static void shouldCompleteProcessing_WhenQueueableEnqueued() {
    Account acc = TestDataFactory.createAccount(true);

    Test.startTest();
    MyQueueableClass queueable = new MyQueueableClass(acc.Id);
    System.enqueueJob(queueable);
    Test.stopTest();

    Account updated = [SELECT Id, Status__c FROM Account WHERE Id = :acc.Id];
    Assert.areEqual('Processed', updated.Status__c,
        'Queueable should update account status');
}

Queueable Chaining

Only the first chained queueable executes in tests. Design tests to verify: 1. First job completes correctly 2. Chain is properly enqueued (query AsyncApexJob) 3. Each job works independently in its own test method

@isTest
static void shouldChainNextJob_WhenMoreRecordsExist() {
    List<Account> accounts = TestDataFactory.createAccounts(500, true);

    Test.startTest();
    MyChainedQueueable queueable = new MyChainedQueueable(0, 100);
    System.enqueueJob(queueable);
    Test.stopTest();

    List<Account> processed = [SELECT Id FROM Account WHERE Processed__c = true];
    Assert.areEqual(100, processed.size(), 'First batch should process 100 records');

    List<AsyncApexJob> jobs = [
        SELECT Id, Status, JobType
        FROM AsyncApexJob
        WHERE ApexClass.Name = 'MyChainedQueueable'
    ];
    Assert.isTrue(jobs.size() >= 1, 'Chained job should be enqueued');
}

Queueable with Callouts

Set the callout mock before Test.startTest():

@isTest
static void shouldMakeCallout_WhenQueueableWithCallout() {
    Test.setMock(HttpCalloutMock.class, new MockHttpResponse(200, '{"status":"ok"}'));
    Account acc = TestDataFactory.createAccount(true);

    Test.startTest();
    MyQueueableWithCallout queueable = new MyQueueableWithCallout(acc.Id);
    System.enqueueJob(queueable);
    Test.stopTest();

    Account updated = [SELECT Id, External_Status__c FROM Account WHERE Id = :acc.Id];
    Assert.areEqual('Synced', updated.External_Status__c,
        'Should update status after successful callout');
}

Future Method Testing

@isTest
static void shouldExecuteFutureMethod() {
    Account acc = TestDataFactory.createAccount(true);

    Test.startTest();
    MyClass.processFuture(acc.Id);
    Test.stopTest();

    Account updated = [SELECT Id, Processed__c FROM Account WHERE Id = :acc.Id];
    Assert.isTrue(updated.Processed__c, 'Future should process record');
}

Scheduled Apex Testing

Direct Execution

@isTest
static void shouldExecuteScheduledJob() {
    List<Account> accounts = TestDataFactory.createAccounts(50, true);

    Test.startTest();
    MyScheduledClass scheduled = new MyScheduledClass();
    scheduled.execute(null);
    Test.stopTest();

    List<Account> processed = [SELECT Id FROM Account WHERE Processed__c = true];
    Assert.areEqual(50, processed.size(), 'Scheduled job should process records');
}

CRON Registration

@isTest
static void shouldScheduleJob() {
    Test.startTest();
    String cronExp = '0 0 6 * * ?';
    String jobId = System.schedule('Daily Processing', cronExp, new MyScheduledClass());
    Test.stopTest();

    CronTrigger ct = [
        SELECT Id, CronExpression, State
        FROM CronTrigger
        WHERE Id = :jobId
    ];
    Assert.areEqual('0 0 6 * * ?', ct.CronExpression, 'CRON should match');
    Assert.areEqual('WAITING', ct.State, 'Job should be waiting');
}

Common Pitfalls

Mocking Patterns

HTTP Callout Mocking

Apex doesn't allow real HTTP callouts in tests. Use HttpCalloutMock interface.

Basic Mock

@isTest
public class MockHttpResponse implements HttpCalloutMock {
    
    private Integer statusCode;
    private String body;
    
    public MockHttpResponse(Integer statusCode, String body) {
        this.statusCode = statusCode;
        this.body = body;
    }
    
    public HTTPResponse respond(HTTPRequest req) {
        HttpResponse res = new HttpResponse();
        res.setStatusCode(statusCode);
        res.setBody(body);
        res.setHeader('Content-Type', 'application/json');
        return res;
    }
}

Using the Mock

@isTest
static void shouldProcessApiResponse_WhenCalloutSucceeds() {
    String mockResponse = '{"status": "success", "data": [{"id": "123"}]}';
    Test.setMock(HttpCalloutMock.class, new MockHttpResponse(200, mockResponse));

    Test.startTest();
    List<ExternalRecord> results = MyIntegrationService.fetchRecords();
    Test.stopTest();

    Assert.areEqual(1, results.size(), 'Should parse one record from response');
    Assert.areEqual('123', results[0].externalId, 'Should extract correct ID');
}

@isTest
static void shouldHandleError_WhenCalloutFails() {
    String errorResponse = '{"error": "Unauthorized"}';
    Test.setMock(HttpCalloutMock.class, new MockHttpResponse(401, errorResponse));

    Test.startTest();
    CalloutResult result = MyIntegrationService.fetchRecords();
    Test.stopTest();

    Assert.areEqual(false, result.isSuccess, 'Should indicate failure');
    Assert.isTrue(result.errorMessage.contains('Unauthorized'), 'Should capture error');
}

Multi-Request Mock

For services making multiple callouts:

@isTest
public class MultiRequestMock implements HttpCalloutMock {

    private Map<String, HttpResponse> endpointResponses;

    public MultiRequestMock(Map<String, HttpResponse> responses) {
        this.endpointResponses = responses;
    }

    public HTTPResponse respond(HTTPRequest req) {
        String endpoint = req.getEndpoint();
        for (String key : endpointResponses.keySet()) {
            if (endpoint.contains(key)) {
                return endpointResponses.get(key);
            }
        }
        HttpResponse res = new HttpResponse();
        res.setStatusCode(404);
        res.setBody('{"error": "Not found"}');
        return res;
    }
}

StaticResourceCalloutMock

Use when response JSON is large or complex:

@isTest
static void shouldParseComplexResponse() {
    StaticResourceCalloutMock mock = new StaticResourceCalloutMock();
    mock.setStaticResource('TestApiResponse');
    mock.setStatusCode(200);
    mock.setHeader('Content-Type', 'application/json');
    Test.setMock(HttpCalloutMock.class, mock);

    Test.startTest();
    Result r = MyService.callExternalApi();
    Test.stopTest();

    Assert.isNotNull(r, 'Should parse response');
}

SOSL Mocking

SOSL returns empty results in tests by default. Call Test.setFixedSearchResults(List<Id>) before the search:

@isTest
static void shouldReturnSearchResults() {
    Account acc = TestDataFactory.createAccount(true);
    Test.setFixedSearchResults(new List<Id>{ acc.Id });

    Test.startTest();
    List<Account> results = MyService.searchAccounts('Test');
    Test.stopTest();

    Assert.areEqual(1, results.size(), 'Should return mocked search result');
}

DML Mocking (Constructor Injection)

Design for testability — use a public constructor for production and a @TestVisible private constructor that accepts mock interfaces:

public class MyService {
    private IDML dmlHandler;

    public MyService() {
        this.dmlHandler = new DMLHandler();
    }

    @TestVisible
    private MyService(IDML dmlHandler) {
        this.dmlHandler = dmlHandler;
    }

    public void createRecords(List<Account> accounts) {
        dmlHandler.doInsert(accounts);
    }
}

Stub API (System.StubProvider)

For mocking Apex class dependencies:

@isTest
public class MyServiceMock implements System.StubProvider {

    public Object handleMethodCall(
        Object stubbedObject, String stubbedMethodName, Type returnType,
        List<Type> paramTypes, List<String> paramNames, List<Object> args
    ) {
        if (stubbedMethodName == 'getAccountData') {
            return new AccountData('Mock Account', 'Active');
        }
        return null;
    }
}

@isTest
static void shouldUseAccountData() {
    MyServiceMock mockProvider = new MyServiceMock();
    IMyService mockService = (IMyService) Test.createStub(IMyService.class, mockProvider);

    MyController controller = new MyController(mockService);

    Test.startTest();
    String result = controller.displayAccountInfo();
    Test.stopTest();

    Assert.isTrue(result.contains('Mock Account'), 'Should use mocked data');
}

Email Testing

Apex doesn't actually send emails in tests. Use limits to verify:

@isTest
static void shouldSendEmail_WhenTriggered() {
    Integer emailsBefore = Limits.getEmailInvocations();

    Test.startTest();
    MyService.sendNotification(testContact);
    Test.stopTest();

    Assert.areEqual(emailsBefore + 1, Limits.getEmailInvocations(),
        'One email should be sent');
}

Platform Event Testing

@isTest
static void shouldPublishEvent_WhenRecordCreated() {
    Test.startTest();
    Test.enableChangeDataCapture();

    Account acc = TestDataFactory.createAccount(true);
    Test.getEventBus().deliver();
    Test.stopTest();
    
    // Query platform event trigger results
    List<EventLog__c> logs = [SELECT Id FROM EventLog__c WHERE AccountId__c = :acc.Id];
    Assert.areEqual(1, logs.size(), 'Event handler should create log record');
}

TestDataFactory Patterns

For the base class template, see assets/test-data-factory-template.cls.

Design Rules

1. Always accept a `doInsert` flag — lets callers modify records before insert 2. Append loop index to all fields that participate in matching rules — prevents DUPLICATES_DETECTED errors from active Duplicate Rules 3. Single-record methods delegate to bulk — e.g., createAccount(doInsert) calls createAccounts(1, doInsert)[0] 4. Return created records — enables chaining and further manipulation 5. Set all required fields — include fields enforced by validation rules, not just schema-required fields

Field Override Pattern

Allow callers to override default values without creating new factory methods:

public static Account createAccount(Map<String, Object> fieldOverrides, Boolean doInsert) {
    Account acc = new Account(
        Name = 'Test Account',
        Industry = 'Technology'
    );
    for (String fieldName : fieldOverrides.keySet()) {
        acc.put(fieldName, fieldOverrides.get(fieldName));
    }
    if (doInsert) insert acc;
    return acc;
}

// Usage:
Account acc = TestDataFactory.createAccount(new Map<String, Object>{
    'Name' => 'Custom Name',
    'Industry' => 'Healthcare'
}, true);

Record Type Support

public static Account createAccountByRecordType(String recordTypeName, Boolean doInsert) {
    Id recordTypeId = Schema.SObjectType.Account
        .getRecordTypeInfosByDeveloperName()
        .get(recordTypeName)
        .getRecordTypeId();

    Account acc = new Account(
        Name = 'Test Account',
        RecordTypeId = recordTypeId
    );
    if (doInsert) insert acc;
    return acc;
}

Handling Duplicate Rules

When unique field values alone are not sufficient, use Database.insert() with a DuplicateRuleHeader:

public static List<Account> createAccountsAllowDuplicates(Integer count, Boolean doInsert) {
    List<Account> accounts = new List<Account>();
    for (Integer i = 0; i < count; i++) {
        accounts.add(new Account(
            Name = 'Test Account ' + i,
            Phone = '555-000-' + String.valueOf(i).leftPad(4, '0')
        ));
    }
    if (doInsert) {
        Database.DMLOptions dml = new Database.DMLOptions();
        dml.DuplicateRuleHeader.allowSave = true;
        Database.insert(accounts, dml);
    }
    return accounts;
}