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Hel rules over Helheim, where the souls unworthy of Valhalla reside. It's also a mock generator for Go.
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Hel is the norse goddess that rules over Helheim, where the souls of those who did not die in battle go.

This little tool is similar; it generates (hopefully simple) mocks of Go interface types and stores them in helheim_test.go (by default).


There are plenty of mock generators out there, but:

  1. I felt like messing more with Go's ast package.
  2. The mock generators that I know about seem to generate complicated mocks, and often generate their mocks as exported types in a separate package.
  • A side note on exported mocks: Exporting mocks seems to, on some projects, encourage the idea that an interface defines everything that a type is capable of. In Go, I find that to be a bad practice; local interfaces should be defined as functionality that the local logic needs, and concrete types implementing said functionality should be passed in. This keeps interfaces very small, which keeps mocks (mostly) simple.



Hel shells out to goimports to set up its import clause(s), so you'll need that installed somewhere in your PATH.

Go Get

Hel is go-gettable: go get

In the near future, I'll set up a CI system which uploads binaries to github releases, as well.


At its simplest, you can just run hel without any options in the directory you want to generate mocks for. Mocks will be saved in a file called helheim_test.go by default.

See hel -h or hel --help for command line options. Most flags allow multiple calls (e.g. -t ".*Foo" -t ".*Bar").

Go Generate

Adding comments for go generate to use Hel is relatively flexible. Some examples:

In a file (e.g. generate.go) in the root of your project:

//go:generate hel --package ./...

The above command would find all exported interface types in the project and generate mocks in helheim_test.go in each of the packages it finds interfaces to mock.

In a file (e.g. generate.go) in each package you want mocks to be generated for:

//go:generate hel

The above command would generate mocks for all exported types in the current package in helheim_test.go

Above each interface type you want a mock for

//go:generate hel --type Foo --output mock_foo_test.go

type Foo interface {
   Foo() string

The above command would generate a mock for the Foo type in mock_foo_test.go

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