feature: tools/testifier

[Antonboom]

The tool that rewrites std testing.T assertions with stretchr/testify.

Example

Before:

func TestEncryptAndDecryptData(t *testing.T) {
	key1, err := CreateRandBytes(kubeadmconstants.CertificateKeySize)
	if err != nil {
		t.Fatal(err)
	}

	key2, err := CreateRandBytes(kubeadmconstants.CertificateKeySize)
	if err != nil {
		t.Fatal(err)
	}
 	// ...
}

After:

func TestEncryptAndDecryptData(t *testing.T) {
	key1, err := CreateRandBytes(kubeadmconstants.CertificateKeySize)
 	require.NoError(t, err)

	key2, err := CreateRandBytes(kubeadmconstants.CertificateKeySize)
 	require.NoError(t, err)
  	// ...
}

P.S. Press 👍 if you think this idea make sense.

[ccoVeille]

Extracted from this comment from maintainer in a PR about adding something to CONTRIBUTING

#77 (comment)

Hi!

1. I meant a more common solution than just fatal replacer.

2. `testifier` proposed to be a separate tool and maybe in separate repo

So the idea in this issue is more than adding new rules.

It might be a separate linter that will detect if code is tests could be replaced by using testify (either if code is partially using testify or simply not using it)