A Complete Introduction to Go Testing

Organization of Test Files

In Go, test files are usually located in the same package as the source files being tested, and follow these naming conventions:

• Source file: xxx.go
• Test file: xxx_test.go

Test file names must end with _test.go so that the Go toolchain can recognize and treat them as test files.

Signature of Test Functions

Test functions must have the following signature:

func TestXxx(t *testing.T) { ... }

• The function name starts with Test, followed by the name of the function or feature being tested (usually with an uppercase initial).
• It takes a single parameter *testing.T, which is used to report test failures and log information.

Writing Test Functions

Basic Example

Suppose there is a simple addition function Add, located in the math.go file:

// math.go
package mathutil

func Add(a, b int) int {
    return a + b
}

The corresponding test file math_test.go can be written as follows:

// math_test.go
package mathutil

import (
    "testing"
)

func TestAdd(t *testing.T) {
    tests := []struct {
        a, b, expected int
    }{
        {1, 2, 3},
        {0, 0, 0},
        {-1, 1, 0},
    }

    for _, tt := range tests {
        result := Add(tt.a, tt.b)
        if result != tt.expected {
            t.Errorf("Add(%d, %d) = %d; expected %d", tt.a, tt.b, result, tt.expected)
        }
    }
}

Using Subtests

Go 1.7 introduced subtests, making it more convenient to run multiple related tests within the same test function:

func TestAdd(t *testing.T) {
    tests := []struct {
        a, b, expected int
    }{
        {1, 2, 3},
        {0, 0, 0},
        {-1, 1, 0},
    }

    for _, tt := range tests {
        t.Run(fmt.Sprintf("%d+%d", tt.a, tt.b), func(t *testing.T) {
            result := Add(tt.a, tt.b)
            if result != tt.expected {
                t.Errorf("Add(%d, %d) = %d; expected %d", tt.a, tt.b, result, tt.expected)
            }
        })
    }
}

Using Table-Driven Tests

Table-driven testing is a common pattern where a set of inputs and expected outputs are defined to test a function’s behavior:

func TestMultiply(t *testing.T) {
    tests := []struct {
        a, b, expected int
    }{
        {2, 3, 6},
        {0, 5, 0},
        {-2, 4, -8},
    }

    for _, tt := range tests {
        t.Run(fmt.Sprintf("%d*%d", tt.a, tt.b), func(t *testing.T) {
            result := Multiply(tt.a, tt.b)
            if result != tt.expected {
                t.Errorf("Multiply(%d, %d) = %d; expected %d", tt.a, tt.b, result, tt.expected)
            }
        })
    }
}

Running Tests

Using go test Command

In the package directory containing the test files, run the following command to execute all tests:

go test

Running Specific Tests

To run a specific test function, you can use the -run parameter, which supports regular expressions:

go test -run TestAdd

Viewing Detailed Output

Use the -v flag to see detailed output for each test function:

go test -v

Running Tests in Parallel

Use t.Parallel() to run test functions concurrently, improving testing efficiency:

func TestSomething(t *testing.T) {
    t.Parallel()
    // test code
}

When running tests, you can specify the number of tests to execute in parallel with -parallel:

go test -parallel 4

Test Coverage

Use go test -cover to check test coverage.

Generate a coverage file:

go test -coverprofile=coverage.out
go tool cover -html=coverage.out

Use go test -cover to check test coverage.

Generate a coverage file:

go test -coverprofile=coverage.out
go tool cover -html=coverage.out

Example: Complete Testing Workflow

Here is a comprehensive example showing how to write, run, and check test coverage.

Source Code

// mathutil/math.go
package mathutil

func Add(a, b int) int {
    return a + b
}

func Multiply(a, b int) int {
    return a * b
}

Test Code

// mathutil/math_test.go
package mathutil

import (
    "testing"
)

func TestAdd(t *testing.T) {
    tests := []struct {
        a, b, expected int
    }{
        {1, 2, 3},
        {0, 0, 0},
        {-1, 1, 0},
    }

    for _, tt := range tests {
        t.Run(fmt.Sprintf("%d+%d", tt.a, tt.b), func(t *testing.T) {
            result := Add(tt.a, tt.b)
            if result != tt.expected {
                t.Errorf("Add(%d, %d) = %d; expected %d", tt.a, tt.b, result, tt.expected)
            }
        })
    }
}

Running Tests and Coverage

go test -v -coverprofile=coverage.out
go tool cover -html=coverage.out

Go provides powerful and concise testing tools, making it very convenient to write and maintain tests. By organizing test files properly, writing testable code, and regularly checking test coverage, developers can ensure code quality and reliability. Combined with continuous integration, automated testing becomes an important means of ensuring project stability.

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