Java – How to force the static block running in each test method

javajunitunit testing

I found static block is running only once when I execute multiple JUnit tests. How can I force it to run for each test method? I am using latest JUnit 4.8.2

Also, according to xUnit design principle, every method should be totally independent on others. Why static block only be executed once?

@Test TestMethod1 () {
       Accounts ac = new Accounts();
       ac.method1(); //kill the thread inside
}

@Test TestMethod2 () {
       Accounts ac = new Accounts();
       ac.method2(); // the thread is no longer available!!
}

class Accounts {
   static {
       // initalize one thread to monitor something
   }
}

This even happens when TestMethod1 and TestMethod2 are in the different Test Classes.

Best Answer

static blocks are only executed on class loading because that is what they are: class initializers. To have a static block run multiple times would require you to unload the class (not an easy thing to do...).

If you need to use static blocks, you can come up with ways to test them. Why not unwrap the block into a public (static) method? All you have to do in that world is test the method:

 static {
      staticInitMethod();
 }

 public static void staticInitMethod(){
      //insert initialization code here
 }

you also might be able to get away with just an ordinary initializer

 {//not static
      //insert initialization code here
 }

Although, the truth is most code doesn't need to use initializers like this at all.

Edit: Turns out Oracle likes the static method approach http://download.oracle.com/javase/tutorial/java/javaOO/initial.html

Related Solutions

How should I unit test multithreaded code

Look, there's no easy way to do this. I'm working on a project that is inherently multithreaded. Events come in from the operating system and I have to process them concurrently.

The simplest way to deal with testing complex, multithreaded application code is this: If it's too complex to test, you're doing it wrong. If you have a single instance that has multiple threads acting upon it, and you can't test situations where these threads step all over each other, then your design needs to be redone. It's both as simple and as complex as this.

There are many ways to program for multithreading that avoids threads running through instances at the same time. The simplest is to make all your objects immutable. Of course, that's not usually possible. So you have to identify those places in your design where threads interact with the same instance and reduce the number of those places. By doing this, you isolate a few classes where multithreading actually occurs, reducing the overall complexity of testing your system.

But you have to realize that even by doing this, you still can't test every situation where two threads step on each other. To do that, you'd have to run two threads concurrently in the same test, then control exactly what lines they are executing at any given moment. The best you can do is simulate this situation. But this might require you to code specifically for testing, and that's at best a half step towards a true solution.

Probably the best way to test code for threading issues is through static analysis of the code. If your threaded code doesn't follow a finite set of thread safe patterns, then you might have a problem. I believe Code Analysis in VS does contain some knowledge of threading, but probably not much.

Look, as things stand currently (and probably will stand for a good time to come), the best way to test multithreaded apps is to reduce the complexity of threaded code as much as possible. Minimize areas where threads interact, test as best as possible, and use code analysis to identify danger areas.

Java – How to test a class that has private methods, fields or inner classes

Update:

Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.

If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.

Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.

Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);

And for fields:

Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);

Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for getDeclaredField.
2. The setAccessible(true) is required to play around with privates.

Best Answer

Related Solutions

How should I unit test multithreaded code

Java – How to test a class that has private methods, fields or inner classes

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