Commit 100af58c authored Mar 07, 2025 by José Expósito Committed by Miguel Ojeda Mar 20, 2025

rust: kunit: allow to know if we are in a test



In some cases, we need to call test-only code from outside the test
case, for example, to mock a function or a module.

In order to check whether we are in a test or not, we need to test if
`CONFIG_KUNIT` is set.
Unfortunately, we cannot rely only on this condition because:
- a test could be running in another thread,
- some distros compile KUnit in production kernels, so checking at runtime
  that `current->kunit_test != NULL` is required.

Forturately, KUnit provides an optimised check in
`kunit_get_current_test()`, which checks CONFIG_KUNIT, a global static
key, and then the current thread's running KUnit test.

Add a safe wrapper function around this to know whether or not we are in
a KUnit test and examples showing how to mock a function and a module.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Co-developed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Co-developed-by: David Gow <davidgow@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/r/20250307090103.918788-4-davidgow@google.com


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

parent c0010452

rust/kernel/kunit.rs

+36 −0

Original line number	Diff line number	Diff line
		@@ -288,11 +288,47 @@ macro_rules! kunit_unsafe_test_suite {
		};
		}

		/// Returns whether we are currently running a KUnit test.
		///
		/// In some cases, you need to call test-only code from outside the test case, for example, to
		/// create a function mock. This function allows to change behavior depending on whether we are
		/// currently running a KUnit test or not.
		///
		/// # Examples
		///
		/// This example shows how a function can be mocked to return a well-known value while testing:
		///
		/// ```
		/// # use kernel::kunit::in_kunit_test;
		/// fn fn_mock_example(n: i32) -> i32 {
		/// if in_kunit_test() {
		/// return 100;
		/// }
		///
		/// n + 1
		/// }
		///
		/// let mock_res = fn_mock_example(5);
		/// assert_eq!(mock_res, 100);
		/// ```
		pub fn in_kunit_test() -> bool {
		// SAFETY: `kunit_get_current_test()` is always safe to call (it has fallbacks for
		// when KUnit is not enabled).
		!unsafe { bindings::kunit_get_current_test() }.is_null()
		}

		#[kunit_tests(rust_kernel_kunit)]
		mod tests {
		use super::*;

		#[test]
		fn rust_test_kunit_example_test() {
		#![expect(clippy::eq_op)]
		assert_eq!(1 + 1, 2);
		}

		#[test]
		fn rust_test_kunit_in_kunit_test() {
		assert!(in_kunit_test());
		}
		}