How to Print Debug Information in Go Tests Using the `testing` Package?

How to print debug information in a Go test using the "testing" package?

When writing Go tests, it is sometimes useful to print debug information to help understand the behavior of your code. However, printing to standard output using fmt.Println() does not work inside tests. This is because test output is buffered and only printed if the test fails.

The "testing" package provides two alternative methods for printing debug information:

• t.Log()
• t.Logf()

These methods are similar to fmt.Print() and fmt.Printf(), but they write their output directly to the test log. To enable logging, you need to specify the -v (verbose) flag when running go test:

go test -v

This will print all log messages to standard output, including those from successful tests.

Here is an example of how to use t.Log() and t.Logf():

func TestPrintSomething(t *testing.T) {
    t.Log("Say hi")
    t.Logf("The value of myVar is %d", myVar)
}

When running this test with -v, the following output will be printed:

=== RUN   TestPrintSomething
Say hi
The value of myVar is 1234
--- PASS: TestPrintSomething (0.00s)

You can also use t.Error() to print an error message. This will cause the test to fail.

Here is an example of how to use t.Error():

func TestPrintSomething(t *testing.T) {
    if myVar != 1234 {
        t.Errorf("The value of myVar is %d, but it should be 1234", myVar)
    }
}

When running this test with -v, the following output will be printed:

=== RUN   TestPrintSomething
The value of myVar is 4567, but it should be 1234
--- FAIL: TestPrintSomething (0.00s)

The testing package also provides a testing.B type for benchmarking tests. The testing.B type has a Log() method that works like t.Log().

Here is an example of how to use B.Log():

func BenchmarkSomething(b *testing.B) {
    for i := 0; i < b.N; i++ {
        // Do something
        b.Log("The value of i is", i)
    }
}

When running this benchmark with go test -v, the following output will be printed:

=== RUN   BenchmarkSomething
The value of i is 0
The value of i is 1
The value of i is 2
The value of i is 3
...
The value of i is 1000
--- BENCH: BenchmarkSomething  1000000000000000000/s

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