testfs

A simple fs.FS which is contained in a test (using testing.TB's TempDir()) and with a few helper methods.

PS: This lib only works on Go 1.16+.

Example

func TestSomething(t *testing.T) {
	tmpfs := testfs.New(t)
	testfile := "foo/bar/foobar"
	_ = tmpfs.MkdirAll(filepath.Dir(testfile), 0o764)
	_ = tmpfs.WriteFile(testfile, []byte("example"), 0o644)

	// you can now use tmpfs as a fs.FS...
	// fs.WalkDir(tmpfs, ".", func(path string, d fs.DirEntry, err error) error { return nil })

	// and read files of course:
	bts, _ := fs.ReadFile(tmpfs, testfile)
	fmt.Println(string(bts))
}

Why

The idea is to able to test code that use a fs.FS, without having to, for example, commit a bunch of files inside testdata and without using in-memory implementation that might not do the same thing as a real FS.

This is a real FS, it only limits itself to a temporary directory and cleans after itself once the test is done. You also get a couple of helper methods to create the structure you need.

Other options

If you don't mind testing against an in-memory implementation, the native fstest.MemFS is a good option.