Table of Contents
Introduction
In Go programming, writing tests is an essential part of ensuring the reliability and correctness of code. However, simply writing tests is not enough; it is equally important to perform proper error checking to catch any unexpected issues or failures.
This tutorial will guide you through the process of error checking in Go tests, providing you with the necessary knowledge and techniques to write robust and reliable tests. By the end of this tutorial, you will understand how to handle errors effectively, improve test coverage, and ensure your tests are resilient and accurate.
Prerequisites
Before you get started with this tutorial, you should have a basic understanding of the Go programming language. Familiarity with writing tests in Go is also beneficial.
Setting up Go
To follow along with this tutorial, you need to have Go installed on your machine. You can download and install the latest version of Go from the official Go website: https://golang.org/dl/
Once Go is installed, you can verify the installation by opening a terminal and running the following command:
go version
If the command returns the installed Go version, you are ready to proceed.
Error Checking in Go Tests
Writing a Basic Test
Let’s start by writing a basic test case in Go. Create a new file named errors_test.go and open it in a text editor. In this example, we’ll write a simple test for a function that divides two integers:
package main
import (
"errors"
"testing"
)
func Divide(a, b int) (int, error) {
if b == 0 {
return 0, errors.New("division by zero")
}
return a / b, nil
}
func TestDivide(t *testing.T) {
result, err := Divide(10, 2)
if err != nil {
t.Errorf("unexpected error: %v", err)
}
if result != 5 {
t.Errorf("expected 5, got %d", result)
}
}
In this test case, we first call the Divide function with valid input and check if the returned error is nil. Then, we check if the result is equal to the expected value. If any of these conditions fail, we report an error using the t.Errorf method.
Handling Errors
Go provides built-in error types, such as error and errors.New, to handle errors. In our example, the Divide function returns an int and an error. We use the errors.New function to create a new error when division by zero occurs.
if b == 0 {
return 0, errors.New("division by zero")
}
When an error occurs, we return zero as the result and the created error. This allows the caller to handle the error appropriately.
Testing Error Scenarios
To test error scenarios in Go, you can use the if err != nil condition to check for errors. In our TestDivide function, we check if the divide function returns an error and fail the test if it does:
result, err := Divide(10, 2)
if err != nil {
t.Errorf("unexpected error: %v", err)
}
By reporting the error using t.Errorf, we provide details about the error when the test fails.
Running the Tests
To run the tests, open a terminal and navigate to the directory containing the errors_test.go file. Then, execute the following command:
go test -v
The -v flag enables verbose output, showing the names and results of each individual test.
If the tests pass, you will see an output similar to the following:
=== RUN TestDivide
--- PASS: TestDivide (0.00s)
PASS
On the other hand, if an error occurs during the test execution, you will see an output with the detailed error message.
Improving Test Coverage
To ensure thorough test coverage, it is important to test both error and non-error scenarios. Let’s enhance our test case to cover the division by zero scenario as well:
func TestDivide(t *testing.T) {
result, err := Divide(10, 2)
if err != nil {
t.Errorf("unexpected error: %v", err)
}
if result != 5 {
t.Errorf("expected 5, got %d", result)
}
_, err = Divide(10, 0)
if err == nil {
t.Error("expected error, got nil")
}
}
In this updated test case, we call the Divide function with the divisor set to zero and check if the returned error is not nil. If the error is nil, we report an error using t.Error.
Running the tests again should now provide improved coverage by testing both error and non-error scenarios.
Common Error Handling Techniques
There are several common error handling techniques used in Go tests:
1. Error Assertion
To check if an error equals a specific value, you can use an error assertion. For example:
expectedError := errors.New("expected error message")
if err != expectedError {
t.Errorf("expected %q, got %q", expectedError, err)
}
2. Error Wrapping
In Go, you can wrap errors using the fmt.Errorf function to provide additional context or details:
if err != nil {
wrappedErr := fmt.Errorf("division failed: %w", err)
return 0, wrappedErr
}
The %w verb is used to wrap the error.
3. Error Testing
When testing error scenarios, you can use the if statement to check for a specific error or error type:
if _, ok := err.(*MyErrorType); !ok {
t.Errorf("expected %T, got %T", &MyErrorType{}, err)
}
By using type assertions, you can validate the error type in your tests.
Troubleshooting Tips and FAQs
Q: Why do we need to write tests?
A: Tests help verify the correctness of your code and catch issues early. They provide confidence when making changes or refactoring existing code.
Q: How can I test a function that writes to standard output?
A: In Go, you can capture the standard output using the os.Stdout variable, and then compare it to the expected value.
func TestPrintHello(t *testing.T) {
old := os.Stdout
r, w, _ := os.Pipe()
os.Stdout = w
PrintHello()
w.Close()
out, _ := ioutil.ReadAll(r)
os.Stdout = old
expected := "Hello, Go!"
if string(out) != expected {
t.Errorf("expected %q, got %q", expected, string(out))
}
}
Q: Can I mock external dependencies in tests?
A: Yes, Go provides various mocking frameworks, such as “gomock” and “testify,” to help you mock external dependencies and control their behavior during tests.
Conclusion
In this tutorial, you learned how to perform effective error checking in Go tests. You now understand how to write robust tests, handle errors, improve test coverage, and use common error handling techniques. Keep practicing and writing tests, as it is crucial for building reliable and maintainable Go applications.
Remember, writing tests is not just about verifying correctness; it is a mindset and a practice that helps you become a better developer.
Happy testing!