afv-library/skills/running-apex-tests/references/performance-optimization.md

Performance Optimization for Apex Tests

Fast tests enable faster development. When test suites run quickly, developers refactor confidently. This guide covers techniques to dramatically reduce test execution time.

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Why Test Speed Matters

Test Suite Duration	Impact
< 5 minutes	Developers run frequently, catch issues early
5-30 minutes	Developers run occasionally, issues slip through
30+ minutes	Developers avoid running, tests become stale
Hours	CI/CD bottleneck, blocked deployments

The goal: Sub-second unit tests, with integration tests taking seconds, not minutes.

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Technique 1: Mock DML Operations

Database operations are the #1 cause of slow tests.

The Numbers

Operation	10,000 Records	Notes
Actual insert	~50 seconds	Database round-trips
DML mocking	<1 second	In-memory only
Improvement	~35x faster

Implementation

See assets/dml-mock.cls and references/mocking-patterns.md for complete implementation.

// ❌ SLOW: Actual database insert
List<Account> accounts = TestDataFactory.createAccounts(1000);
insert accounts;  // ~5 seconds

// ✅ FAST: Mock DML
DMLMock.reset();
AccountService service = new AccountService(new DMLMock());
service.createAccounts(accounts);  // <0.1 seconds
Assert.areEqual(1000, DMLMock.InsertedRecords.size());

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Technique 2: Mock SOQL Queries

Query execution adds overhead, especially with large result sets.

// ❌ SLOW: Actual query requiring test data setup
@TestSetup
static void setup() {
    List<Account> accounts = new List<Account>();
    for (Integer i = 0; i < 1000; i++) {
        accounts.add(new Account(Name = 'Test ' + i));
    }
    insert accounts;  // Slow
}

// ✅ FAST: Mock query results
AccountSelector.setMockResults(new List<Account>{
    new Account(Name = 'Mock 1'),
    new Account(Name = 'Mock 2')
});
List<Account> results = AccountSelector.getActiveAccounts();  // Instant

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Technique 3: Minimize @TestSetup

@TestSetup runs before every test method. Large setups compound execution time.

// ❌ SLOW: Heavy @TestSetup
@TestSetup
static void setup() {
    List<Account> accounts = TestDataFactory.createAccounts(100);
    insert accounts;
    List<Contact> contacts = TestDataFactory.createContacts(500, accounts);
    insert contacts;
    List<Opportunity> opps = TestDataFactory.createOpportunities(200, accounts);
    insert opps;
    // Total: 800 DML operations, runs before EACH test method
}

// ✅ FAST: Minimal @TestSetup, mock what you can
@TestSetup
static void setup() {
    // Only create what MUST exist in database
    Account parentAccount = new Account(Name = 'Required Parent');
    insert parentAccount;
}

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Technique 4: Choose Efficient Loop Constructs

Loop performance varies significantly with large iterations.

Benchmark Results (10,000 iterations)

Loop Type	Duration	Notes
While loop	~0.4s	Fastest
Cached iterator	~0.8s	Good alternative
For loop (index)	~1.4s	Acceptable
Enhanced for loop	~2.4s	Convenient but slower
Uncached iterator	CPU limit	Avoid

Recommendation

// ✅ PREFERRED: While loop for large iterations
Iterator<Account> iter = accounts.iterator();
while (iter.hasNext()) {
    Account acc = iter.next();
    // process
}

// ✅ ACCEPTABLE: Standard for loop
for (Integer i = 0; i < accounts.size(); i++) {
    Account acc = accounts[i];
    // process
}

// ⚠️ CONVENIENT BUT SLOWER: Enhanced for
for (Account acc : accounts) {
    // process
}

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Technique 5: Batch Test Data Creation

Creating records one-by-one is slow. Batch operations are faster.

// ❌ SLOW: One-by-one creation
for (Integer i = 0; i < 200; i++) {
    Account acc = new Account(Name = 'Test ' + i);
    insert acc;  // 200 DML statements!
}

// ✅ FAST: Batch creation
List<Account> accounts = new List<Account>();
for (Integer i = 0; i < 200; i++) {
    accounts.add(new Account(Name = 'Test ' + i));
}
insert accounts;  // 1 DML statement

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Technique 6: Use Assert Instead of System.assert

The modern Assert class is cleaner and provides better error messages.

// ❌ OLD: System.assert (still works but verbose)
System.assert(result != null, 'Result should not be null');
System.assertEquals(expected, actual, 'Values should match');

// ✅ MODERN: Assert class (Apex 56.0+)
Assert.isNotNull(result, 'Result should not be null');
Assert.areEqual(expected, actual, 'Values should match');
Assert.isTrue(condition, 'Condition should be true');
Assert.fail('Should not reach here');

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Technique 7: Avoid SOSL in Tests

SOSL searches return empty results in tests unless configured.

// ❌ PROBLEM: SOSL returns nothing in tests by default
List<List<SObject>> results = [FIND 'test' IN ALL FIELDS RETURNING Account];
// results[0] is EMPTY even with matching records!

// ✅ SOLUTION: Use Test.setFixedSearchResults()
@IsTest
static void testSearch() {
    Account acc = new Account(Name = 'Searchable');
    insert acc;

    // Configure what SOSL will return
    Test.setFixedSearchResults(new List<Id>{ acc.Id });

    Test.startTest();
    List<List<SObject>> results = [FIND 'test' IN ALL FIELDS RETURNING Account];
    Test.stopTest();

    Assert.areEqual(1, results[0].size(), 'Should find configured record');
}

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Technique 8: Strategic Test Method Scoping

Run only the tests you need during development.

# ❌ SLOW: Run all tests (minutes to hours)
sf apex run test --test-level RunLocalTests --target-org sandbox

# ✅ FAST: Run single test class
sf apex run test --class-names MyClassTest --target-org sandbox

# ✅ FASTER: Run single test method
sf apex run test --tests MyClassTest.testSpecificMethod --target-org sandbox

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Technique 9: Async Test Execution

Use async mode for large test suites to avoid blocking.

# Start tests asynchronously
sf apex run test --class-names MyClassTest --wait 0 --target-org sandbox
# Returns test run ID: 707xx0000000000

# Check status later
sf apex get test --test-run-id 707xx0000000000 --target-org sandbox

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Anti-Patterns to Avoid

Anti-Pattern	Problem	Solution
DML in loops	N operations instead of 1	Bulk DML outside loops
Large @TestSetup	Runs before every test	Minimize or mock
No mocking	Full database round-trips	Mock DML, queries, callouts
SeeAllData=true	Depends on org data	Create test data
Deep nested loops	O(n²) or worse	Flatten with Maps
String concatenation in loops	New string objects each iteration	Use List and join

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Optimization Checklist

Before committing tests, verify:

• DML operations are mocked where possible
• @TestSetup is minimal
• No SOQL/DML inside loops
• Uses bulk patterns (200+ records)
• Individual test methods run in <1 second
• Full test class runs in <10 seconds
• Uses Assert class (not System.assert)

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Performance Testing Your Tests

@IsTest
static void testPerformance() {
    Long startTime = System.currentTimeMillis();

    // Your test code here

    Long duration = System.currentTimeMillis() - startTime;
    System.debug('Test duration: ' + duration + 'ms');

    // Assert performance constraint
    Assert.isTrue(duration < 1000, 'Test should complete in <1 second, took: ' + duration + 'ms');
}