我知道有一种方法是:
@Test
public void foo() {
try {
// execute code that you expect not to throw Exceptions.
} catch(Exception e) {
fail("Should not have thrown any exception");
}
}
还有更干净的方法吗?(可能使用了Junit的@Rule?)
我知道有一种方法是:
@Test
public void foo() {
try {
// execute code that you expect not to throw Exceptions.
} catch(Exception e) {
fail("Should not have thrown any exception");
}
}
还有更干净的方法吗?(可能使用了Junit的@Rule?)
当前回答
我偶然发现这一点是因为SonarQube的规则“squid:S2699”:“向这个测试用例添加至少一个断言。”
我有一个简单的测试,它的唯一目标是不抛出异常。
考虑这段简单的代码:
public class Printer {
public static void printLine(final String line) {
System.out.println(line);
}
}
可以添加什么样的断言来测试这个方法? 当然,您可以尝试捕获它,但这只是代码膨胀。
解决方案来自JUnit本身。
如果没有抛出异常,并且你想显式地说明这种行为,只需添加预期,如下例所示:
@Test(expected = Test.None.class /* no exception expected */)
public void test_printLine() {
Printer.printLine("line");
}
Test.None.class是预期值的默认值。
如果您导入org.junit.Test。没有,你可以这样写:
@Test(expected = None.class)
你可能会觉得更有可读性。
其他回答
如果您不幸捕获了代码中的所有错误。 你可以愚蠢地做
class DumpTest {
Exception ex;
@Test
public void testWhatEver() {
try {
thisShouldThrowError();
} catch (Exception e) {
ex = e;
}
assertEquals(null,ex);
}
}
以下是所有检查或未检查的异常都无法通过测试:
@Test
public void testMyCode() {
try {
runMyTestCode();
} catch (Throwable t) {
throw new Error("fail!");
}
}
如果您想测试您的测试目标是否使用异常。只需要将测试保留为(使用jMock2的模拟合作者):
@Test
public void consumesAndLogsExceptions() throws Exception {
context.checking(new Expectations() {
{
oneOf(collaborator).doSth();
will(throwException(new NullPointerException()));
}
});
target.doSth();
}
如果您的目标确实使用抛出的异常,则测试将通过,否则测试将失败。
如果您想测试异常使用逻辑,事情会变得更加复杂。我建议将消费委托给一个可能被嘲笑的合作者。因此,测试可以是:
@Test
public void consumesAndLogsExceptions() throws Exception {
Exception e = new NullPointerException();
context.checking(new Expectations() {
{
allowing(collaborator).doSth();
will(throwException(e));
oneOf(consumer).consume(e);
}
});
target.doSth();
}
但如果你只是想记录它,有时它就设计过度了。在这种情况下,如果您坚持使用tdd,本文(http://java.dzone.com/articles/monitoring-declarative-transac, http://blog.novoj.net/2008/09/20/testing-aspect-pointcuts-is-there-an-easy-way/)可能会有所帮助。
使用assertNull(…)
@Test
public void foo() {
try {
//execute code that you expect not to throw Exceptions.
} catch (Exception e){
assertNull(e);
}
}
Java 8让这变得容易多了,Kotlin/Scala更是如此。
我们可以写一个小工具类
class MyAssertions{
public static void assertDoesNotThrow(FailingRunnable action){
try{
action.run()
}
catch(Exception ex){
throw new Error("expected action not to throw, but it did!", ex)
}
}
}
@FunctionalInterface interface FailingRunnable { void run() throws Exception }
然后你的代码就变得很简单:
@Test
public void foo(){
MyAssertions.assertDoesNotThrow(() -> {
//execute code that you expect not to throw Exceptions.
}
}
如果你不能使用java -8,我会使用一种非常古老的java工具:任意的代码块和一个简单的注释
//setup
Component component = new Component();
//act
configure(component);
//assert
/*assert does not throw*/{
component.doSomething();
}
最后,用kotlin,一种我最近爱上的语言:
fun (() -> Any?).shouldNotThrow()
= try { invoke() } catch (ex : Exception){ throw Error("expected not to throw!", ex) }
@Test fun `when foo happens should not throw`(){
//...
{ /*code that shouldn't throw*/ }.shouldNotThrow()
}
尽管有很多空间可以随意改变你想要如何表达这一点,但我一直喜欢流畅的断言。
关于
你想错了。只需测试您的功能:如果抛出异常,测试将自动失败。如果没有抛出异常,您的测试将全部显示为绿色。
这在原则上是正确的,但在结论上是不正确的。
Java允许控制流的异常。这是由JRE运行时本身在Double等api中完成的。parseDouble通过NumberFormatException和路径。通过invalidpatheexception获取。
Given you've written a component that validates Number strings for Double.ParseDouble, maybe using a Regex, maybe a hand-written parser, or perhaps something that embeds some other domain rules that restricts the range of a double to something specific, how best to test this component? I think an obvious test would be to assert that, when the resulting string is parsed, no exception is thrown. I would write that test using either the above assertDoesNotThrow or /*comment*/{code} block. Something like
@Test public void given_validator_accepts_string_result_should_be_interpretable_by_doubleParseDouble(){
//setup
String input = "12.34E+26" //a string double with domain significance
//act
boolean isValid = component.validate(input)
//assert -- using the library 'assertJ', my personal favourite
assertThat(isValid).describedAs(input + " was considered valid by component").isTrue();
assertDoesNotThrow(() -> Double.parseDouble(input));
}
我还鼓励您使用Theories或Parameterized对输入参数化这个测试,这样您就可以更容易地对其他输入重复使用这个测试。或者,如果您想要与众不同,您可以使用测试生成工具(以及这个工具)。TestNG对参数化测试有更好的支持。
What I find particularly disagreeable is the recommendation of using @Test(expectedException=IllegalArgumentException.class), this exception is dangerously broad. If your code changes such that the component under test's constructor has if(constructorArgument <= 0) throw IllegalArgumentException(), and your test was supplying 0 for that argument because it was convenient --and this is very common, because good generating test data is a surprisingly hard problem--, then your test will be green-bar even though it tests nothing. Such a test is worse than useless.