AssertEquals

AssertEquals is a common unit testing assertion used to verify that two values are equal. It is provided by many testing frameworks and is essential for validating the expected outcomes of code under test. The exact function name, signature, and rules vary by language, but the core idea remains the same: compare an expected value to an actual value and fail the test if they differ.

In Java's JUnit, the method is Assert.assertEquals(expected, actual), with overloads for primitive types and a delta parameter for floating-point comparisons. If the values are not equal, the assertion fails and reports the expected and actual values. In PHP's PHPUnit, the equivalent is $this->assertEquals($expected, $actual, $message), which uses PHP's loose equality by default; a stricter variant exists as assertSame. In .NET testing frameworks such as NUnit or MSTest, the analogous assertion is Assert.AreEqual(expected, actual), often with overloads and optional tolerance for numeric types.

Semantics vary by type: for objects, equality typically depends on the type’s definition of equality (for example, a language’s equals method in Java, or operator behavior in PHP). For collections, frameworks may perform deep equality checks or rely on element-wise comparison as defined by the framework. Floating-point comparisons commonly require a tolerance to account for rounding error.

Usage notes include providing a descriptive failure message and avoiding brittle tests by using appropriate equality checks or specialized assertions for approximate or deep equality.