fsmock

A golang mock implementation of fs.FS and friends for testing.

fsmock implements a mock filesystem satisfying fs.FS and other interfaces to enable easier testing of code that uses fs.FS to access file systems.

Installation

fsmock is provided as a go module and requires go >= 1.16.

go get github.com/halimath/fsmock@main

Usage

fsmock provides two basic types Dir and File. These can be used to build up a filesystem in plain go. Use the provided functions NewDir and NewFile to create them conveniently.

Create a new filesystem by invoking fsmock.New providing a root directory.

fsys := fsmock.New(fsmock.NewDir("",
    fsmock.EmptyFile("go.mod"),
    fsmock.EmptyFile("go.sum"),
    fsmock.NewDir("cmd",
        fsmock.TextFile("main.go", "package main"),
    ),
    fsmock.NewDir("internal",
        fsmock.EmptyFile("tool.go"),
        fsmock.EmptyFile("tool_test.go"),
    ),
))

You can use the methods defined in fs.FS and other interfaces from the fs package to access files and directories:

f, err := fsys.Open("cmd/main.go")
if err != nil {
    panic(err)
}

fs.WalkDir(fsys, "", func(path string, d fs.DirEntry, err error) error {
    // ...
    return nil
})

Modifying the filesystem

In addition to the read-only functions defined by the fs interfaces, fsmock provides some helper functions to modify the filesystem.

To update a modification timestamp of either a file or directory use the Touch function. This will also create an empty file if the named file does not exist (just like the Unix touch command does):

if err := fsys.Touch("internal/foo/foo.go"); err != nil {
    panic(err)
}

To create a directory use the Mkdir function which works like the mkdir Unix shell command (without the -p option):

if err := fsys.Mkdir("internal/foo"); err != nil {
    panic(err)
}

See fsmock_test.go for a full-blown example.

License

Copyright 2022 Alexander Metzner.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.