Generating Apex Test

/**
 * Test class for {ClassUnderTest}.
 * Tests bulk operations (251+ records), positive/negative paths,
 * and exception handling.
 */
@isTest
private class {ClassUnderTest}Test {

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

    // ─── Positive Tests ───────────────────────────────────────────────────

    @isTest
    static void shouldPerformExpectedBehavior_WhenValidInput() {
        // Given
        List<Account> accounts = [SELECT Id, Name FROM Account];

        // When
        Test.startTest();
        // {ClassUnderTest}.methodUnderTest(params);
        Test.stopTest();

        // Then
        // Assert.areEqual(expected, actual, 'Descriptive failure message');
    }

    @isTest
    static void shouldHandleBulkRecords_WhenProcessing251() {
        // Given
        List<Account> accounts = [SELECT Id FROM Account];
        Assert.areEqual(251, accounts.size(), 'Should have 251 test records');

        // When
        Test.startTest();
        // {ClassUnderTest}.bulkMethod(accounts);
        Test.stopTest();

        // Then
        // List<Account> results = [SELECT Id, Status__c FROM Account];
        // for (Account acc : results) {
        //     Assert.areEqual('Processed', acc.Status__c, 'All records should be processed');
        // }
    }

    // ─── Negative Tests ───────────────────────────────────────────────────

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

    @isTest
    static void shouldReturnEmpty_WhenEmptyInput() {
        Test.startTest();
        // List<SObject> results = {ClassUnderTest}.methodUnderTest(new List<Id>());
        Test.stopTest();

        // Assert.isTrue(results.isEmpty(), 'Should return empty list for empty input');
    }

    // ─── Edge Case Tests ──────────────────────────────────────────────────

    @isTest
    static void shouldHandleMixedRecords_WhenSomeQualify() {
        // Given
        List<Account> accounts = [SELECT Id, Status__c FROM Account];
        Integer half = accounts.size() / 2;
        // for (Integer i = 0; i < half; i++) {
        //     accounts[i].Status__c = 'Qualifying';
        // }
        // update accounts;

        // When
        Test.startTest();
        // {ClassUnderTest}.conditionalMethod(accounts);
        Test.stopTest();

        // Then
        // List<Account> qualifying = [SELECT Id FROM Account WHERE Processed__c = true];
        // Assert.areEqual(half, qualifying.size(), 'Only qualifying records should be processed');
    }
}


/**
 * @description Centralized factory for creating test data with sensible defaults.
 *              All methods accept a doInsert flag for flexibility.
 *              Bulk methods create multiple records; single-record methods delegate to bulk.
 */
@isTest
public class TestDataFactory {

    // ─── Accounts ─────────────────────────────────────────────────────────

    public static List<Account> createAccounts(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,
                BillingCity = 'San Francisco',
                BillingState = 'CA',
                BillingCountry = 'USA',
                Industry = 'Technology',
                Type = 'Customer'
            ));
        }
        if (doInsert) insert accounts;
        return accounts;
    }

    public static Account createAccount(Boolean doInsert) {
        return createAccounts(1, doInsert)[0];
    }