capsules: add capsule test error

capsules/core/src/test/capsule_test.rs

@@ -5,8 +5,9 @@
 //! Interface for running capsule tests.
 //!
 //! As Tock capsules are asynchronous, it is difficult for a test runner to
-//! determine when a test when a test has finished. This interface provides a
-//! `done()` callback to notify when the test is done.
+//! determine when a test has finished. This interface provides a `done()`
+//! callback used by the test implementation to notify when the test has
+//! completed.
 //!
 //! A simple example of a test capsule using this interface:
 //!
@@ -39,11 +40,26 @@
 //! }
 //! ```
 
+use kernel::ErrorCode;
+
+/// Errors for the result of a failed test.
+pub enum CapsuleTestError {
+    /// The test computed some result (e.g., a checksum or hash) and the result
+    /// is not correct (e.g., it doesn't match the intended value, say the
+    /// correct checksum or hash).
+    IncorrectResult,
+
+    /// An error occurred while running the test, and the resulting `ErrorCode`
+    /// is provided.
+    ErrorCode(ErrorCode),
+}
+
 /// Client for receiving test done events.
 pub trait CapsuleTestClient {
-    /// Called when the test is finished. If test was successful, `result` is
-    /// `Ok(())`. If test failed, `result` is `Err(())`.
-    fn done(&'static self, result: Result<(), ()>);
+    /// Called when the test is finished. If the test was successful, `result`
+    /// is `Ok(())`. If the test failed, `result` is `Err()` with a suitable
+    /// error.
+    fn done(&'static self, result: Result<(), CapsuleTestError>);
 }
 
 /// Identify a test as a capsule test. This is only used for setting the client