Junit 实例精讲基础教程（二） 使用@Test+expected、@Rule+ExpectedException模拟方法异常执行的方式

在实际业务中，进行单元测试时，我们除了需要测试正常流程和正确的程序功能之外，可能还需要测试异常场景，在Junit中该如何模拟异常场景呢？

更多精彩请阅读 东陆之滇的csdn博客：http://blog.csdn.net/zixiao217

在Junit中，通常有3种方式去模拟生产中的异常场景。

使用@Test结合它的属性expected

使用try-catch并且最后使用fail()

使用@Rule和 ExpectedException

1. 使用@Test和其属性expected

Exception1Test.java:

package org.byron4j.spring_mvc_log4j.mock;

import java.util.ArrayList;

import org.junit.Test;

public class Exception1Test {

/**
* 如果测试该方法时产生一个ArithmeticException的异常，则表示测试通过
* 你可以改成int i = 1 / 1;运行时则会测试不通过-因为与你的期望的不符
*/
@Test(expected = ArithmeticException.class)
public void testDivisionWithException() {
int i = 1 / 0;
}

/**
* 运行时抛出一个IndexOutOfBoundsException异常才会测试通过
*/
@Test(expected = IndexOutOfBoundsException.class)
public void testEmptyList() {
new ArrayList<>().get(0);
}
}

2. try-catch并且总是在块最后加上fail()

Exception2Test.java:

package org.byron4j.spring_mvc_log4j.mock;

import java.util.ArrayList;

import org.junit.Test;

//注意：这是java中的静态引入
import static junit.framework.TestCase.fail;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.MatcherAssert.assertThat;

public class Exception2Test {
@Test
public void testDivisionWithException() {
try {
int i = 1 / 0;

fail();
} catch (ArithmeticException e) {
assertThat(e.getMessage(), is("/ by zero"));

}
}

@Test
public void testEmptyList() {
try {
new ArrayList<>().get(0);
fail();
} catch (IndexOutOfBoundsException e) {
assertThat(e.getMessage(), is("Index: 0, Size: 0"));
}
}
}

3. 使用@Rule和ExpectedException

ExpectedException

从4.7之后才有的，可以让你测试到异常类型和异常信息。可以认为和try-catch+fail()，但是更优雅些。

Exception3Test.java:

package org.byron4j.spring_mvc_log4j.mock;

import static org.hamcrest.CoreMatchers.containsString;
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.Matchers.hasProperty;

import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;

public class Exception3Test {
@Rule
public ExpectedException thrown = ExpectedException.none();

@Test
public void testDivisionWithException() {

thrown.expect(ArithmeticException.class);
thrown.expectMessage(containsString("/ by zero"));

int i = 1 / 0;

}

@Test
public void testNameNotFoundException() throws NameNotFoundException {

//test type
thrown.expect(NameNotFoundException.class);

//test message
thrown.expectMessage(is("Name is empty!"));

//test detail
thrown.expect(hasProperty("errCode"));  //make sure getters n setters are defined.
thrown.expect(hasProperty("errCode", is(666)));

CustomerService cust = new CustomerService();
cust.findByName("");

}

}

自定义的异常类NameNotFoundException.java：

package org.byron4j.spring_mvc_log4j.mock;

public class NameNotFoundException extends Exception{
private int errCode;

public NameNotFoundException(int errCode, String message) {
super(message);
this.errCode = errCode;
}

public int getErrCode() {
return errCode;
}

public void setErrCode(int errCode) {
this.errCode = errCode;
}
}

CustomerService.java:

package org.byron4j.spring_mvc_log4j.mock;

public class CustomerService {
public Customer findByName(String name) throws NameNotFoundException {

if ("".equals(name)) {
throw new NameNotFoundException(666, "Name is empty!");
}

return new Customer(name);

}

static class Customer{
private String name;

public Customer(String name) {
super();
this.name = name;
}

}
}