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Does JUnit4 testclasses require a public no arg constructor?

Asked 2009-09-20T17:20:24.427
11

I have a test class, written in JUnit4 syntax, that can be run in eclipse with the "run as junit test" option without failing. When I run the same test via an ant target I get this error:

java.lang.Exception: Test class should have public zero-argument constructor
at org.junit.internal.runners.MethodValidator.validateNoArgConstructor(MethodValidator.java:54)
at org.junit.internal.runners.MethodValidator.validateAllMethods(MethodValidator.java:39)
at org.junit.internal.runners.TestClassRunner.validate(TestClassRunner.java:33)
at org.junit.internal.runners.TestClassRunner.<init>(TestClassRunner.java:27)
at org.junit.internal.runners.TestClassRunner.<init>(TestClassRunner.java:20)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at org.junit.internal.requests.ClassRequest.getRunner(ClassRequest.java:26)
at junit.framework.JUnit4TestAdapter.<init>(JUnit4TestAdapter.java:24)
at junit.framework.JUnit4TestAdapter.<init>(JUnit4TestAdapter.java:17)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.run(JUnitTestRunner.java:386)
at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.launch(JUnitTestRunner.java:911)
at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.main(JUnitTestRunner.java:768)
Caused by: java.lang.NoSuchMethodException: dk.gensam.gaia.business.bonusregulering.Te
java ant junit
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2 Answers

5

You must have a default constructor for the test case. Otherwise, the runner doesn't know how to instantiate the class. Looks like you have a constructor with args. Java doesn't create default constructor if you already have a constructor.

Generally, you should avoid constructors in test cases. If you want do initialization, write a init method and annotate it with @BeforeClass. The benefit is that the stack trace will be much cleaner if you have any errors. As you can see, the constructor's stack trace is really confusing for most people.

answered 2009-09-20T18:11:54.757
1

Having a no-arg constructor allows test classes to be aggregated into suites:

 TestSuite suite = new TestSuite();
 suite.add(TestClass.class);
 ...
answered 2009-09-20T18:05:19.870

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