如何使用JUnit進行單元測試時處理異常？

Question

如果一個方法拋出異常，如何編寫一個測試用例來驗證該方法實際上是否拋出了預期的異常？

Answer 1

在最新版本的JUnit中，它以這種方式工作：

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

public class NumberFormatterExceptionsTests {

    @Rule
    public ExpectedException thrown = ExpectedException.none();

    @Test
    public void shouldThrowExceptionWhenDecimalDigitsNumberIsBelowZero() {
        thrown.expect(IllegalArgumentException.class); // you declare specific exception here
        NumberFormatter.formatDoubleUsingStringBuilder(6.9, -1);
    }
}

更多關於ExpectedExceptions：

http://kentbeck.github.com/junit/javadoc/4.10/org/junit/rules/ExpectedException.html

http://alexruiz.developerblogs.com/?p=1530

// These tests all pass.
 public static class HasExpectedException {
        @Rule
        public ExpectedException thrown= ExpectedException.none();

        @Test
        public void throwsNothing() {
    // no exception expected, none thrown: passes.
        }

        @Test
        public void throwsNullPointerException() {
                thrown.expect(NullPointerException.class);
                throw new NullPointerException();
        }

        @Test
        public void throwsNullPointerExceptionWithMessage() {
                thrown.expect(NullPointerException.class);
                thrown.expectMessage("happened?");
                thrown.expectMessage(startsWith("What"));
                throw new NullPointerException("What happened?");
        }
 }

Answer 2

我知道的兩個選項。

如果使用junit4

@Test(expected = Exception.class)

或者如果使用junit3

try {
    methodThatThrows();
    fail("this method should throw excpetion Exception");
catch (Exception expect){}

這兩個都捕獲異常。 我建議捕獲您正在尋找的異常而不是通用異常。

Answer 3

您可以嘗試捕獲所需的異常並執行類似assertTrue(true) ：

@Test
testIfThrowsException(){
    try{
        funcThatShouldThrowException(arg1, agr2, agr3);
        assertTrue("Exception wasn't thrown", false);
    }
    catch(DesiredException de){
        assertTrue(true);
    }
}