How to Effectively Debug Go Tests Using Logging?

Debugging Go Tests with Logging

When writing Go tests, you might want to print statements for debugging purposes. However, unlike regular programs, prints inside tests do not appear directly on the screen.

Using testing.T.Log and testing.T.Logf

The testing package provides T.Log and T.Logf methods, which are equivalent to fmt.Print and fmt.Printf, respectively. These methods direct logs to a specific buffer, which can be accessed with the -v (verbose) flag when running tests.

Example

func TestPrintSomething(t *testing.T) {
    t.Log("Say hi")
}

When run with go test -v, this test will output:

=== RUN   TestPrintSomething
Say hi
--- PASS: TestPrintSomething (0.00s)

Differences from fmt.Print

While fmt.Print statements appear directly on the console, T.Log and T.Logf logs are buffered. This means that:

• Logs for successful tests are only shown when the -v flag is used.
• Logs for failed tests are always shown, regardless of the -v flag.

Conclusion

To print statements in Go tests, use testing.T.Log or testing.T.Logf instead of fmt.Print. This ensures that your logs are directed to the correct buffer and displayed appropriately.

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