廖雪峰Java8JUnit单元测试-2使用JUnit-2异常测试

1.异常测试

对可能抛出的异常进行测试：

• 异常本身是方法签名的一部分：
  
  * public static int parseInt(String s) throws NumberFormatException
• 测试错误的输入是否导致特定的异常：
  
  * Integer.parseInt(null)
  
  * Integer.parseInt("")
  
  * Integer.parseInt("xyz")

2.异常测试的方法：

• 使用try..catch (Exception e)捕获异常，但这样会编写许多try..catch代码
• expected测试异常，推荐

2.1示例1

package com.testList;

import org.junit.*;

import static org.junit.Assert.fail;

public class SequenceTest {
    //使用try...catch
    @Test
    public void test1() throws Exception{
        try {
            Integer.parseInt(null);
            fail("should throw java.lang.NumberFormatException");
        }catch (NumberFormatException e){
            System.out.println("pass");
        }
    }
    //使用expected捕获异常
    @Test(expected = NumberFormatException.class)
    public void test2() throws Exception{
        Integer.parseInt("p");
    }
}

### 2.2示例2
Calculator.java
```#java
package com.testList;

public class Calculator {

public int calculator(String expression){

if (expression == null){

throw new NumberFormatException();

}

String[] ss = expression.split("\+");

int sum = 0;

for(String s:ss){

sum = sum + Integer.parseInt(s.trim());

}

return sum;

}

}

CalculatorTest.java
```#java
package com.testList;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.util.Calendar;

import static org.junit.Assert.*;

public class CalculatorTest {
    Calculator calc;
    @Before
    public void setUp(){
        calc = new Calculator();
    }
    @Test(expected = NumberFormatException.class)
    public void testCalcWithEmptyString(){
        int r = calc.calculator("");
    }
    @Test(expected =NumberFormatException.class)
    public void testCalcAdd3Numbers(){
        int r = calc.calculator(null);
    }
    @After
    public void tearDown(){
        calc = null;
    }
}

3.总结

• 测试异常可以使用@Test(expected = Exception.class)
• 对可能发生的每种类型的异常进行测试