Assertions Worth Knowing

An assertion compares the expected value with the actual one and stops the test with a readable message when they differ. Prefer the strictest one that fits:

The PHPUnit 13 79,198 assertions you will use most
Assertion	Passes when
assertSame	===: same type and value, same instance
assertEquals	==: equal value objects, but also '10' and 10
assertArraysAreIdenticalIgnoringOrder	same pairs in any order (new in 13)
assertJsonStringEqualsJsonString	two JSON documents are equivalent

Here is a deliberately wrong expectation, to show what a failure looks like:

tests/Unit/QuantitiesTest.php, a test that fails on purposePHP

<?php
use PHPUnit\Framework\TestCase;
use Shop\{Money, Order, Product};
final class QuantitiesTest extends TestCase {
  public function testQuantitiesAfterTwoAdds(): void {
    $order = new Order();
    $order->add(new Product('BK-PHP-01', 'Modern PHP in Practice', new Money(3990), 25), 2);
    $order->add(new Product('AC-MUG-01', 'Semicolon Coffee Mug', new Money(1250), 60), 1);
    $this->assertSame(['BK-PHP-01' => 2, 'AC-MUG-01' => 2], $order->quantities());
  }
}

Output

...
1) QuantitiesTest::testQuantitiesAfterTwoAdds
Failed asserting that two arrays are identical.
--- Expected
+++ Actual
@@ @@
 Array &0 [
     'BK-PHP-01' => 2,
-    'AC-MUG-01' => 2,
+    'AC-MUG-01' => 1,
 ]
/home/dev/bookshop/tests/Unit/QuantitiesTest.php:10
...

The diff marks the expected line - and the actual +, then gives the failing line. Correct the expectation to 1 and the test passes.

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Assertions Worth Knowing