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Fake vs Mock

An example that shows the use of test doubles, ie. fakes and mocks, in Go unit testing.

Definition

Fake and mock are collectively called test doubles.

  • Fake - Fake doesn't modify the behavior of the system under test. There are 2 forms of fakes:
    • Fake data - Use non-real (fake) data eg. [email protected]
    • Fake system - Instead of using an actual system dependency in production, eg. Postgres or MySQL, the test suite uses a simpler system, eg. simple SQLite, to mimic the actual system.
  • Mock - You have components in your system that call or depend on another dependency. A mock allows the tester to mock that dependency and assert that your system has interacted with the dependency. This recipe provides examples for 2 popular mock frameworks:
    • Gomock - This is a framework that generates mock code at build time.
    • Testify Mock - This is a framework that relies on reflection to generate mocks at runtime.

Read here for an explanation on fake vs mock.

Project Description

This example is based on a forgot password web service, which generates a random password and replaces the existing password in the system. The main components are:

  • Account - The representation of the user's account in the system.
  • AccountModel - The data access layer that creates, fetches, and deletes a user's account.
  • AccountService - The API endpoint, from which the user can call to reset his/her password.

In unit test api_test.go, we see that the test is using both a fake and mock:

  • Test using a fake - We emulate data access to a SQL database with in-code map data type. Note: it probably more relevant using SQLite to fake the SQL database access layer than Golang map
  • Test using a mock - We mock the AcccountModel with MockAccountModel.

Setup

  1. Install mockgen

    $ make install

  2. Generate the mocks.

    $ make mockgen

  3. Run the test

    $ go test -v ./api

  4. Alternatively, just run everything with the following command:

    $ make install   # Optional: run this if you haven't installed mockgen
$ make  # Run all the above commands

Reference