assertSame

AssertSame is a unit testing assertion used to verify the identity of two values or references. The precise meaning depends on the testing framework and language, but it generally tests for referential identity or exact sameness rather than mere value equality. An assertion with the same name in different ecosystems may thus have slightly different semantics.

In PHP's PHPUnit, assertSame($expected, $actual, $message = '') checks that $expected === $actual. For scalars, this means identical value and type. For objects, it requires that both references point to the same instance. It is stricter than assertEquals, which uses value equality (==) and may involve type coercion or deep comparisons.

In Java's JUnit, assertSame(Object expected, Object actual) asserts that expected == actual, i.e., the two references refer to the same object in memory. For value equality, JUnit provides assertEquals, which delegates to the equals method of the objects. Primitive values can be involved through autoboxing, but the essence remains referential identity rather than content equality.

A companion assertion, assertNotSame, is used to verify that two references do not refer to the same object. When writing tests, assertSame is appropriate when the identity of an object matters—for example, when a method must return a particular singleton instance or when reusing a cached object.

See also: assertNotSame, assertEquals, assertIs (in some languages).