Golang Unit Testing

Testing is a crucial part of software development and Go support for testing was built right into the language itself by providing a testing packages along with the command line tool, go test, to run test suites. The standard tool-chain also includes benchmarking and statement based code coverage.

1. Unit Testing

Coming from the other languages, testing in Go might feel a little bit out of place as the syntax deliberately avoids the use of assertions and leaves the responsibility for checking values and behaviour to the developer. Here is an example.

// main.go
package main

func Sum(x, y int) int {
    return x + y
}

// main_test.go
package main

import "testing"

func TestSum(t *testing.T) {
    sum := Sum(10, 20)
    if sum != 30 {
        t.Fail()
    }
}

To write test in Go you need to follow a fews rules

1. Put test code into a separate file name ended in _test.go
2. There is only one parameter for test function and it needs to be *testing.T
3. Each function must begin with Test follow by a word or phrase starting with a capital letter
4. Call one of T function such as t.Fail or t.Error to indicate testing failure

The test code can be placed into the same package or different package.

2. Testing Table

A testing table is a set of test cases where each entry in the table is a complete test case with input, output and expected value. This help remove the needs of copy and paste as you cover many difference cases.

func TestSum(t *testing.T) {
    table := []struct{
        x int
        y int
        n int
    }{
        {1,2,3},
        {2,3,5},
        {3,4,7},
    }
    
    for _, row := range table {
        n := Sum(row.x, row.y)
        if n != row.n {
            t.Errorf("Sum of %d + %d was not equal to %d. Got %d",
            row.x, row.y, row.n, n)
        }
    }
}

3. Run the Test

There are two ways to run test. One is to run the test in the same directory this will pick up any test files in current directory

$ go test

or run it with fully qualify package name like this

$ go test some/package/path

to get a verbos output append -v flag to the above command.

You may feel a little awkward leaving the test files in the same package, but rest assured Go won't pick them up when you build your application.

4. Code Coverage

The go test has built-in support for code coverage as well. To try out with the above example just append -cover flag. It will gives something similar to the following output.

$ go test -cover
PASS
coverage: 50.0% of statements
ok  	tt	0.005s

There is an other cool feature to Go go test and that is the ability to generate HTML coverage report. Take the above testing for example, to generate html content run these two commands.

$ go test -cover -coverprofile=coverage.prof
$ go tool cover -html=coverage.prof -o coverage.html

You can open the html file and see which part of your code is covered and which part isn't.