Understand Function Pointers and Their Role in CMock
Function pointers allow flexibility in calling functions at runtime, which can be crucial in embedded systems for memory optimization and dynamic behavior.
CMock is used in mocking functions for unit tests, especially when dependencies need control over inputs, outputs, or behavior. Handling function pointers might be tricky due to their dynamic nature.
Common Issues with Function Pointers in CMock
Misconfigured mocks for function pointers can lead to test failures or segmentation faults.
Lack of proper setup to handle callbacks or unexpected interactions during tests can lead to undetected issues.
Solution Technique: Proper Mocking of Function Pointers
Example: Handling and Mocking a Function Pointer
Suppose you have a function that uses a callback for completion:
typedef void (*CallbackFunction)(int status);
void performAction(CallbackFunction callback);
To mock this function in CMock, follow these steps:
- Configure the Mock Correctly:
- Use CMock's Mock Config file (.yml) to specify that
performAction should be mocked.
- Ensure the function handling the
CallbackFunction type is configured to handle pointers.
:cmock:
:mock_prefix: Mock
:plugins:
- callback
- Implement the Mock with Appropriate Callbacks:
// Mocked function with callback
void performAction_CMockExpectAndComplete(CallbackFunction callback) {
// Assume a successful operation and invoke the callback
if (callback != NULL) {
callback(0); // Call with a status code, e.g., '0' for success.
}
}
- Set Up Your Test to Utilize the Callback:
void test_performAction_CallsCallbackWithSuccess(void) {
// Arrange: Create a mock callback function
CallbackFunction myCallback = myCallbackMock;
// Expect the function call and set the callback
performAction_CMockExpectAndComplete(myCallback);
// Act: Call the function under test
performAction(myCallback);
// Assert: Verify that the callback was called as expected
TEST_ASSERT_TRUE(callbackWasCalledCorrectly);
}
Debugging and Validation
Utilize verbose output from CMock to help understand how your mocks are being called during runtime.
If unexpected behavior occurs, specifically check the order of calls and parameters being passed to ensure the flow is as intended.
Use additional plugins like ceedling to enhance the validation and testing process.
Advanced Considerations
For complex scenarios where multiple function pointers or callbacks are chained, consider writing detailed mock and callback handlers to simulate complex interactions.
Always ensure to clean up any dynamically allocated resources or state between tests to prevent cross-test pollution.
Document the expected behaviors and limitations of your mock implementations, especially if they diverge significantly from the actual implementations.
By addressing these aspects, you should be equipped to handle function pointers effectively using CMock, enabling robust and reliable tests for your embedded firmware projects.
