How to Test Go Code with Dependencies

Introduction
Prerequisites
Setting Up Go
Understanding Dependencies
Testing Go Code with Dependencies - Using Mocking Libraries - Creating Test Doubles
Conclusion

Introduction

In Go programming, testing plays a crucial role in ensuring the correctness of your code. However, when your code has dependencies, such as external libraries or services, testing can become complex. This tutorial will guide you through the process of testing Go code with dependencies, providing various techniques and tools to overcome these challenges. By the end of this tutorial, you will be able to effectively test Go code that relies on external dependencies.

Prerequisites

To follow this tutorial, you should have a basic understanding of the Go programming language. Familiarity with concepts like functions, packages, and writing tests in Go will be helpful. Additionally, you will need Go installed on your machine. You can download and install Go from the official Go website (https://golang.org/dl/).

Setting Up Go

Before diving into testing Go code with dependencies, ensure that you have Go properly installed and configured on your machine. Here are the steps to set up Go:

Download the Go distribution suitable for your operating system from the official Go website.
Follow the installation instructions provided for your operating system.
Configure the Go environment variables. Add the Go binary directory to your system’s PATH variable.

To verify that Go is installed correctly, open a terminal and run the following command:
```
 go version
```
If you see the Go version printed, it means Go is successfully installed and configured on your machine.

Understanding Dependencies

Before we can test Go code with dependencies, let’s briefly understand what dependencies are. Dependencies in Go refer to external packages or libraries that your code relies on to perform specific actions or provide functionality.

Go uses a built-in package manager called go modules to manage dependencies. When using go modules, you specify the dependencies required by your project in a go.mod file. The go command can then automatically fetch the necessary packages from the internet and build your code with the required dependencies.

It’s important to separate the concerns of testing and dependencies. When testing, it’s beneficial to isolate your code from its dependencies to ensure that the tests focus solely on the code under test. This can be achieved through various techniques like mocking or creating test doubles.

Testing Go Code with Dependencies

Now, let’s explore different approaches to test Go code with dependencies.

Using Mocking Libraries

One popular approach is to use mocking libraries to create fake, or “mocked,” versions of your dependencies. These mocked dependencies can then be used in the test environment to simulate the behavior of the real dependencies.

There are several mocking libraries available for Go, such as testify/mock and gomock. In this tutorial, we will use testify/mock as an example.

To install the testify/mock library, run the following command:

go get github.com/stretchr/testify/mock

Once installed, you can create mock versions of your dependencies by creating a separate file (e.g., mocks.go) in your test package. Define and implement the mocked versions of the dependent interfaces in this file using the mocking library.

Here’s a simple example:

package mypackage

type MyDependency interface {
    Foo() string
}

type MyService struct {
    Dependency MyDependency
}

func (s *MyService) Bar() string {
    result := s.Dependency.Foo()
    // Perform some logic using the result
    return result
}

To test MyService without the actual MyDependency, create a mocked version of MyDependency using testify/mock:

package mypackage_test

import (
    "testing"

    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/mock"

    "your/package/mypackage"
)

type MockDependency struct {
    mock.Mock
}

func (m *MockDependency) Foo() string {
    args := m.Called()
    return args.String(0)
}

func TestMyService_Bar(t *testing.T) {
    mockDependency := new(MockDependency)
    service := mypackage.MyService{Dependency: mockDependency}

    // Set expectations on the mock dependency
    mockDependency.On("Foo").Return("mocked result")

    result := service.Bar()

    assert.Equal(t, "expected result", result, "result should match the expected value")

    // Assert that the expectations were met
    mockDependency.AssertExpectations(t)
}

In the above example, we create a mock of MyDependency, set expectations on the Foo method, and assert that the expectations were met.

By utilizing mocking libraries, you can easily stub out or fake the behavior of your dependencies, allowing you to write comprehensive tests for your code.

Creating Test Doubles

Another approach to testing Go code with dependencies is by using test doubles. A test double is a simplified implementation of a dependency that behaves similarly to the real dependency but is specifically designed for testing purposes.

There are different types of test doubles, such as stubs, spies, and fakes. Let’s focus on stubs for now, which provide canned responses for method calls.

To create a stub for a dependency, you can either manually create a separate implementation that satisfies the interface or use anonymous functions to define the behavior.

Here’s an example using an anonymous function stub:

package mypackage_test

import (
    "testing"

    "your/package/mypackage"
)

type StubDependency struct{}

func (s *StubDependency) Foo() string {
    return "stubbed result"
}

func TestMyService_Bar(t *testing.T) {
    stubDependency := &StubDependency{}
    service := mypackage.MyService{Dependency: stubDependency}

    result := service.Bar()

    assert.Equal(t, "expected result", result, "result should match the expected value")
}

In the above example, we create a StubDependency struct that satisfies the MyDependency interface. The Foo method of StubDependency returns a canned response, allowing us to control the behavior of the dependency during testing.

Using test doubles can provide more control and flexibility in how dependencies interact with your code during testing.

Conclusion

Testing Go code with dependencies is a vital aspect of ensuring the overall quality and reliability of your application. With the techniques and tools demonstrated in this tutorial, you can effectively test Go code that depends on external packages or services. Whether you choose mocking libraries or test doubles, understanding how to isolate dependencies and control their behavior during testing will improve the robustness of your tests and boost the confidence in your code.

In this tutorial, we covered the following topics:

Setting up Go and understanding its basic requirements.
Explaining the concept of dependencies in Go and their management with go modules.
Introducing different techniques to test Go code with dependencies, including mocking libraries and test doubles.

Now, you have the knowledge and tools to confidently test your Go code, even when it relies on external dependencies. Happy testing!

Published: 20 January 2023