Write a Dagger Function to Test a Go Project

In the previous challenge, you learned how to create a Dagger module with a few dummy Dagger Functions in it. Now you will need to create a more useful module - one that can run the unit tests of a Go project.

The sample Go project is located in ~/todolist. Explore it, paying special attention to the Makefile. After that, in the project's root directory, bootstrap a Dagger module. The module should have only one Dagger Function, which performs the go test command. The function should take in the project's root directory and two optional arguments:

The filter expression to run only the matching tests (default: an empty string, meaning all tests).
The number of times to run the test suite (default: an empty string, meaning the -count flag of the go test command is not set).

The solution checker will use the following commands to verify the implementation:

# Assuming the PWD is the project's root directory

dagger call test --src . stdout
dagger call test --src . --run NoSuchTest stdout
dagger call test --src . --run CreateTodo --count 10 stdout

Make sure the test function runs only the unit tests of the project because the e2e suite would require spinning up the dependencies (e.g. a database).

Good luck!

Hint 1 💡

Don't know where to start? Check out this post on writing Dagger Functions.

Hint 2 💡

The function should conform to the following signature:

import (
  "dagger/todolist/internal/dagger"
)

type Todolist struct{}

func (m *Todolist) Test(
  src *dagger.Directory,
  // +optional
  run string,
  // +optional
  count string,
) *dagger.Container {
  // Your implementation goes here...
}

The above is Go code, but you're free to use any of the supported languages.

Hint 3 💡

Even though Dagger Functions are written in full-blown programming languages, they often look like a bunch of shell commands glued together with Go (or Python, or TypeScript, or whatever). Something still has to execute that go test command.

Hint 4 💡

Tried executing the go test command directly from the test function and it failed? To be able to run the go test command, you need a proper Go development environment, and the function's runtime is definitely not suitable for that.

Dagger uses additional containers to provision required environments for every command execution. Here is what you can do:

func (m *Todolist) Test(
  src *dagger.Directory,
  // +optional
  run string,
  // +optional
  count string,
) *dagger.Container {
  return dag.Container().
    From("golang:1").
      WithDirectory("/src", src).
      WithExec([]string{"go", "test", "..."})
    ...
}