How to test the main package functions in golang?

Question

I want to test a few functions that are included in my main package, but my tests don't appear to be able to access those functions.

My sample main.go file looks like:

package main

import (
    "log"
)

func main() {
    log.Printf(foo())
}

func foo() string {
    return "Foo"
}

and my main_test.go file looks like:

package main

import (
    "testing"
)

func Foo(t testing.T) {
    t.Error(foo())
}

when I run go test main_test.go I get

# command-line-arguments
.\main_test.go:8: undefined: foo
FAIL    command-line-arguments [build failed]

As I understand, even if I moved the test file elsewhere and tried importing from the main.go file, I couldn't import it, since it's package main.

What is the correct way of structuring such tests? Should I just remove everything from the main package asides a simple main function to run everything and then test the functions in their own package, or is there a way for me to call those functions from the main file during testing?

Answer 1

when you specify files on the command line, you have to specify all of them

Here's my run:

$ ls
main.go     main_test.go
$ go test *.go
ok      command-line-arguments  0.003s

note, in my version, I ran with both main.go and main_test.go on the command line

Also, your _test file is not quite right, you need your test function to be called TestXXX and take a pointer to testing.T

Here's the modified verison:

package main

import (
    "testing"
)

func TestFoo(t *testing.T) {
    t.Error(foo())
}

and the modified output:

$ go test *.go
--- FAIL: TestFoo (0.00s)
    main_test.go:8: Foo
FAIL
FAIL    command-line-arguments  0.003s

Answer 2

Change package name from main to foobar in both sources. Move source files under src/foobar.

mkdir -p src/foobar
mv main.go main_test.go src/foobar/

Make sure to set GOPATH to the folder where src/foobar resides.

export GOPATH=`pwd -P`

Test it with

go test foobar

Answer 3

Unit tests only go so far. At some point you have to actually run the program. Then you test that it works with real input, from real sources, producing real output to real destinations. For real.

If you want to unit test a thing move it out of main().