build-web-application-with-golang/en/eBook/11.3.md

# 11.3 Writing test cases

In the course of development, a very important step is to test our code to ensure its quality and integrity. We need to make sure that every function returns the expected result, and that our code performs optimally. We already know that the focus of unit tests is to find logical errors in the design or implementation of programs. They are used to detect and expose problems in code early on so that we can more easily fix them, before they get out of hand. We also know that performance tests are conducted for the purpose of optimizing our code so that it is stable under load, and can maintain a high level of concurrency. In this section, we'll take a look at some commonly asked questions about how unit and performance tests are implemented in Go.     

The Go language comes with a lightweight testing framework called `testing`, and we can use the `go test` command to execute unit and performance tests. Go's `testing` framework works similarly to testing frameworks in other languages. You can develop all sorts of test suites with them, which may include tests for edge cases, benchmarking, etc. Let's learn about testing in Go, step by step.       

## How to write test cases

Since `go test` command can only be executed under a corresponding directory of all files, so we are going to create a new project directory `gotest`, so that all of our code and test code are in this directory.

Next, we create two files in the directory below: gotest.go and gotest_test.go

1. Gotest.go: The document which we have created a package, which has a function in a division operation:

	<pre>package gotest
	
	import (
		"errors"
	)
	
	func Division(a, b float64) (float64, error) {
		if b == 0 {
			return 0, errors.New("Divisor can not be 0")
		}
		return a / b, nil
	}</pre>

2. Gotest_test.go: This is our unit test files, but keep the following principles:

- File names must be `_test.go` end, so in the implementation of `go test` will be executed when the appropriate code
- You have to import `testing` this package
- All test cases functions must be the beginning of `Test`
- Test case will follow the source code written in the order execution
- Test function `TestXxx()` argument is `testing.T`, we can use this type to record errors or test status
- Test format: `func TestXxx(t * testing.T)`, `Xxx` section can be any combination of alphanumeric, but can not be the first letter lowercase letters [az], for example, `Testintdiv` wrong function name.
- Function by calling `testing.T` a `Error`, `Errorf`, `FailNow`, `Fatal`, `FatalIf` method, the test is not passed, calling `Log` test method is used to record the information.

Here is our test code:

	package gotest

	import (
		"testing"
	)

	func Test_Division_1(t *testing.T) {
		// try a unit test on function
		if i, e := Division(6, 2); i != 3 || e != nil { 
			// If it is not as expected, then the error
			t.Error("division function tests do not pass ") 
		} else {
			// record some of the information you expect to record
			t.Log("first test passed ") 
		}
	}

	func Test_Division_2(t *testing.T) {
		t.Error("just do not pass")
	}


We perform in the project directory `go test`, it will display the following information:

	--- FAIL: Test_Division_2 (0.00 seconds)
	gotest_test.go: 16: is not passed
	FAIL
	exit status 1
	FAIL gotest 0.013s
	
From this result shows the test does not pass, because in the second test function we wrote dead do not pass the test code `t.Error`, then our first case of how a function performs like it ? By default, execute `go test` is not displayed test information, we need to bring arguments `go test-v`, this will display the following information:

	=== RUN Test_Division_1
	--- PASS: Test_Division_1 (0.00 seconds)
	gotest_test.go: 11: first test passed
	=== RUN Test_Division_2
	--- FAIL: Test_Division_2 (0.00 seconds)
	gotest_test.go: 16: is not passed
	FAIL
	exit status 1
	FAIL gotest 0.012s
	
The above output shows in detail the process of this test, we see that the test function 1 `Test_Division_1` test, and the test function 2 `Test_Division_2` test fails, finally concluded that the test is not passed. Next we modified the test function 2 the following code:

	func Test_Division_2(t *testing.T) {
		// try a unit test on function
		if _, e := Division(6, 0); e == nil { 
			// If it is not as expected, then the error
			t.Error("Division did not work as expected.") 
		} else {
			// record some of the information you expect to record
			t.Log("one test passed.", e) 
		}
	}

Then we execute `go test-v`, the following information is displayed, the test passes:

	=== RUN Test_Division_1
	--- PASS: Test_Division_1 (0.00 seconds)
	gotest_test.go: 11: first test passed
	=== RUN Test_Division_2
	--- PASS: Test_Division_2 (0.00 seconds)
	gotest_test.go: 20: one test passed. divisor can not be 0
	PASS
	ok gotest 0.013s

## How to write stress test

Stress testing is used to detect function ( method ) performance, and writing unit functional testing method similar are not mentioned here, but need to pay attention to the following points:

- Pressure test must follow the following format, where XXX can be any combination of alphanumeric, but can not be the first letter lowercase letters

	func BenchmarkXXX (b *testing.B){...}

- `Go test` does not default to perform stress tests of function, if you want to perform stress tests need to bring arguments `-test.bench`, syntax: `-test.bench =" test_name_regex "`, such as `go test-test. bench = ". *" ` all of the stress test indicates the test function
- In the pressure test, please remember to use the loop body `testing.BN`, so that the test can be normal operation
- File name must end with `_test.go`

Here we create a stress test file webbench_test.go, the code is as follows:

	package gotest

	import (
		"testing"
	)

	func Benchmark_Division(b *testing.B) {
		for i := 0; i < bN; i++ { // use bN for looping
			Division(4, 5)
		}
	}

	func Benchmark_TimeConsumingFunction(b *testing.B) {
		b.StopTimer() // call the function to stop the stress test time count

		// Do some initialization work, such as reading file data, database connections and the like,
		// So we test these times do not affect the performance of the function itself

		b.StartTimer() // re- start time
		for i := 0; i < b.N; i++ {
			Division(4, 5)
		}
	}



We execute the command `go test-file webbench_test.go-test.bench =". * "`, You can see the following results:

	PASS
	Benchmark_Division 500000000 7.76 ns/ op
	Benchmark_TimeConsumingFunction 500000000 7.80 ns/ op
	ok gotest 9.364s

The above results show that we did not perform any `TestXXX` unit test functions, the results show only a function of stress tests carried out, the first show `Benchmark_Division` executed 500 million times the average execution time is 7.76 ns, the second shows the `Benchmark_TimeConsumingFunction` executed 500 million each, the average execution time is 7.80 ns. Finally a show total execution time.

## Summary

On the face of unit testing and stress testing of learning, we can see the `testing` package is very lightweight, and write unit tests and stress test is very simple, with built-in `go test` command can be very convenient for testing, so every time we have finished modifying code, click go test execution can simply complete regression testing.

## Links

- [Directory](preface.md)
- Previous section: [Debugging by using GDB](11.2.md)
- Next section: [Summary](11.4.md)