Junit官方入门指南

This small example shows you how to write a unit test. You need to have a JDK installed and a text editor. (In general it is recommended to use a build tool for building your software and running the tests.)

一个简单的展示你如何去写一个单元测试。你需要安装一个JDK和一个文本编辑器（比较推荐使用一个构建工具，用于构建你的软件和运行的测试）

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Preparation 准备工作

Create a new folder junit-example and download the current junit-4.XX.jar from JUnit’s release page and Hamcrest to this folder.

创建一个文件 junit-example 并且下载 junit相关的jar包刚在该目录下，下载地址

Change to the folder junit-example. All files are created within this folder and all commands are executed there, too.

当改变junit-example文件时，这个文件夹里所有创建的文件和所有命令也都会被执行。

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Create the class under test 创建一个类，用来测试

Create a new file Calculator.java and copy the following code to this file.

创建一个文件 Calculator.java，并且拷贝如下代码到该文件中

public class Calculator {  public int evaluate(String expression) {    int sum = 0;    for (String summand: expression.split("\\+"))      sum += Integer.valueOf(summand);    return sum;  }}

Now compile this class: 编译这个类文件

javac Calculator.java

The Java compiler creates a file Calculator.class.

这个java 编辑器创建了一个文件 Calculator.class.

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Create a test 创建一个测试

Create the file CalculatorTest.java and copy the following code to this file.

创建一个文件 CalculatorTest.java 并且复制下面代码到文件中

import static org.junit.Assert.assertEquals;import org.junit.Test;public class CalculatorTest {  @Test  public void evaluatesExpression() {    Calculator calculator = new Calculator();    int sum = calculator.evaluate("1+2+3");    assertEquals(6, sum);  }}

Compile the test. On Linux or MacOS

编译这个test在Linux 或者 MackOS上

javac -cp .:junit-4.XX.jar alculatorTest.java

and on Windows

在windows上

javac -cp .;junit-4.XX.jar alculatorTest.java

The Java compiler creates a file >CalculatorTest.class.
java编译器创建一个文件 CalculatorTest.class.

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Run the test 运行测试

Run the test from the command line. On Linux or MacOS

在 Linux 或者 Macos 环境下，从命令行中运行test

java -cp .:junit-4.XX.jar:hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest

nd on Windows

在windows环境下

java -cp .;junit-4.XX.jar;hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest

The output is

输出结果

JUnit version 4.12.Time: 0,006OK (1 test)

The single . means that one test has been run and the OK in the last line tells you that your test is successful.

这一个 . 的意思是，这个测试已经被运行，并且成功运行到最后一行，告诉你你的测试时成功的。

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Let the test fail 测试失败

Modify Calculator.java in order to get a failing test. Replace the line

修改 Calculator.java 为了获得一个错误的测试，替换这一行

sum += Integer.valueOf(summand);

with 用这个替换

sum -= Integer.valueOf(summand);

and recompile the class.

并且重新编译类文件

javac Calculator.java

Run the test again. On Linux or MacOS

重复运行测试，在linux 或者Macos上

java -cp .:junit-4.XX.jar:hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest

and on Windows

在windows 上

java -cp .;junit-4.XX.jar;hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest

Now the test fails and the output is

现在测试失败，并且输出

JUnit version 4.12.ETime: 0,007There was 1 failure:1) evaluatesExpression(CalculatorTest)java.lang.AssertionError: expected:<6> but was:<-6>  at org.junit.Assert.fail(Assert.java:88)  ...FAILURES!!!Tests run: 1,  Failures: 1

JUnit tells you which test failed (evaluatesExpression(CalculatorTest)) and what went wrong:

Junit 告诉你那个测试失败，evaluatesExpression(CalculatorTest) 和 什么出错了

java.lang.AssertionError: expected:<6> but was:<-6>

意思是，断言出错了，，应该是6，，但是结果却是-6