CODEWITHSUNDEEP
javaeclipsegradlejunitjar
isobretatel
isobretatel

Reputation: 3958

How do I test Java code that uses JAR?

I have Java code that uses JAR:

public class Version {
   public String getVersion() {
        // Use Java Package API to return information specified in the manifest of this JAR.
        return getClass().getPackage().getImplementationVersion();
    }
}

How do I run JUnit test for this code?

It fails in development build (in Eclipse) since there is no JAR file yet.

It fails in production build (in Gradle) since there is no JAR file yet.

Upvotes: 0

Views: 1138

Answers (2)

GhostCat
GhostCat

Reputation: 140633

Chances are, that this can't be properly mocked (and thus: not unit tested). The point is that you are actually calling a method on "this". But you can't test some object ... and mock it at the same time.

You see, if your production code would look like this:

public String getVersion() {
    return someObject.getClass().....
}

then you could create a mock object; and insert that into your Version class. But even then, the method getClass() is final within java.lang.Object; and therefore you can't be mocking it anyway.

[ Reasonable mocking frameworks like EasyMock or Mokito work by extending classes and overriding the methods you want to control. There are frameworks like PowerMock that do byte code manipulation and that allow for this kind of mocking - but you should never ever use such libraries; as they have really bad side effects (like breaking most coverage libraries) ]

What might work:

class Version {
    private final Package packageForVersionCheck;

    public Version() {
      this(getClass().getPackage()));
    }
    Version(Package somePackage) {
      this.packageForVersionCheck = ...
    }

    public String getVersion() {
      return this.packageForVersionCheck.getImpl....

Now you can use dependency injection to provide a "mocked" package that returns that string. But well, that looks like a lot of code for almost no gain.

Long story short: sometimes, you simply can't write a reasonable unit test. Then do the next best thing: create some "functional" test that is automatically executed in a "customer like" setup; and make sure that you have an automated setup to run such tests, too.

Upvotes: 1

lazydev
lazydev

Reputation: 432

You always need to mock the dependencies for your unit testing. Boundary is unit test your code and not the jar itself. Mockito framework is good and there are other frameworks that do the job.

Upvotes: 1

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