From 100af58c8d5822750ef9ba65f5d5ea3367c669de Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Jos=C3=A9=20Exp=C3=B3sito?= Date: Fri, 7 Mar 2025 17:00:58 +0800 Subject: [PATCH] rust: kunit: allow to know if we are in a test MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Co-developed-by: Miguel Ojeda Signed-off-by: Miguel Ojeda Co-developed-by: David Gow Signed-off-by: David Gow Link: https://lore.kernel.org/r/20250307090103.918788-4-davidgow@google.com Signed-off-by: Miguel Ojeda --- rust/kernel/kunit.rs | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/rust/kernel/kunit.rs b/rust/kernel/kunit.rs index 50cd45912d6e..1604fb6a5b1b 100644 --- a/rust/kernel/kunit.rs +++ b/rust/kernel/kunit.rs @@ -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()); + } }