Assertions and Common Patterns
By the end of this lesson, you'll be able to:
- Use System.assertEquals, assertNotEquals, and assert to verify behavior
- Follow the arrange-act-assert pattern for readable tests
Prerequisites: Setting Up Test Data
The core assertion methods
System.assertEquals(expected, actual, [message]), System.assertNotEquals(...), and System.assert(condition, [message]) cover almost everything you'll need. Always pass the expected value first and the actual value second — the failure message reads correctly that way. The optional message argument makes a failing test much faster to diagnose.
Arrange, Act, Assert
Structure every test method in three visible phases: arrange (build the data), act (call exactly the thing you're testing), assert (check the outcome). One logical behavior per test method — not a dozen unrelated assertions crammed into a single giant test.
A test in three clear phases
@isTest
static void discountedPriceAppliesTenPercentOff() {
// Arrange
Decimal originalPrice = 100;
// Act
Decimal result = PricingService.applyDiscount(originalPrice, 0.10);
// Assert
System.assertEquals(90, result, 'A 10% discount on 100 should be 90');
}The three phases stay visually separated even without comments once you get used to the pattern — it's what makes a failing test easy to diagnose at a glance.
Exercise
Write a test asserting that MathHelper.isEven(4) returns true and MathHelper.isEven(3) returns false.
Show hint
Use System.assert() for booleans, negating it for the false case.
Assertions and Common Patterns — Quick Check
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Summary
System.assertEquals(expected, actual) is the workhorse assertion; structuring every test as arrange (set up data), act (call the code under test), assert (check the result) keeps tests readable and focused on one behavior each.