How Can I Achieve Full Test Coverage for Go Functions Using `os.Exit()` with Coveralls?

Testing os.Exit scenarios in Go with coverage information (coveralls.io/Goveralls)

This question discusses the limitations of testing os.Exit scenarios in Go using the method of reinvoking the binary and checking the exit value. While this method is effective for testing os.Exit() calls, it poses challenges when it comes to coverage testing with tools like coveralls.io and Goveralls.

The primary issue stems from the fact that the reinvoked binary does not run with the -cover flag, which is necessary for coverage information to be collected. As a result, coverage testing tools fail to recognize that the tested function, Crasher(), which calls os.Exit(), has been executed.

To address this problem, the proposed solution involves refactoring the code to make the os.Exit or log.Fatalf functions replaceable. By saving the original function and restoring it after the test, the test code can intercept these functions and execute them under controlled conditions.

In the provided example, a custom myExit function is defined to replace os.Exit and a custom myFatalf function to replace log.Fatalf. Within the test, these functions are executed and their arguments are captured. This allows the test to verify the correct exit code or log message, ensuring that the tested function is indeed being executed as expected.

By following this approach, it is possible to obtain full coverage of the tested function, even when it involves calling os.Exit() or log.Fatalf(). This enables developers to thoroughly test their code and ensure that the coverage information reported by tools like coveralls.io and Goveralls is accurate and complete.

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