Use `assertNotNull(obj)`. `assert` means `must be`. 

The `assertNotNull()` method means &quot;a passed parameter must not be `null`&quot;: if it is null then the test case fails.  
The `assertNull()` method means &quot;a passed parameter must be `null`&quot;: if it is not null then the test case fails.  

    String str1 = null;
    String str2 = &quot;hello&quot;;              

    // Success.
    assertNotNull(str2);

    // Fail.
    assertNotNull(str1);

    // Success.
    assertNull(str1);

    // Fail.
    assertNull(str2);

`assertNotNull` asserts that the object is not null.  If it is null the test fails, so you want that.

I just want to add that if you want to write special text if It null than you make it like that

      Assert.assertNotNull(&quot;The object you enter return null&quot;, str1)



I&#39;m trying to write a simple code with a `setTimeout`, but the `setTimeout` just won&#39;t wait the time it&#39;s supposes to and the code execute immediately. What am I doing wrong?

    setTimeout(testfunction(), 2000);

Why is the method executed immediately when I use setTimeout?

How can I fill a multidimensional array in Java without using a loop? I&#39;ve tried:

    double[][] arr = new double[20][4];
    Arrays.fill(arr, 0);

This results in `java.lang.ArrayStoreException: java.lang.Double`

Arrays.fill with multidimensional array in Java

This is a pretty dumb question but my first time with unit testing so:
lets say I have an object variable like obj and I want my unit test to Fail if this obj is Null.
so for assertions, should I say AssertNull or AssertNotNull ? I get confused how they are named.

AssertNull should be used or AssertNotNull

<p>This is a pretty dumb question but my first time with unit testing so:
lets say I have an object variable like obj and I want my unit test to Fail if this obj is Null.
so for assertions, should I say AssertNull or AssertNotNull ? I get confused how they are named.</p>


I am trying to create a signature using the HMAC-SHA256 algorithm and this is my code.
I am using US ASCII encoding.

    final Charset asciiCs = Charset.forName(&quot;US-ASCII&quot;);
    final Mac sha256_HMAC = Mac.getInstance(&quot;HmacSHA256&quot;);
    final SecretKeySpec secret_key = new javax.crypto.spec.SecretKeySpec(asciiCs.encode(&quot;key&quot;).array(), &quot;HmacSHA256&quot;);
    sha256_HMAC.init(secret_key);
    final byte[] mac_data = sha256_HMAC.doFinal(asciiCs.encode(&quot;The quick brown fox jumps over the lazy dog&quot;).array());
    String result = &quot;&quot;;
    for (final byte element : mac_data)
    {
        result += Integer.toString((element &amp; 0xff) + 0x100, 16).substring(1);
    }
    System.out.println(&quot;Result:[&quot; + result + &quot;]&quot;);

The result that I am getting from the above code is:

    f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8

This is same as to that of shown in the wiki

    HMAC_SHA256(&quot;key&quot;, &quot;The quick brown fox jumps over the lazy dog&quot;) = 0x f7bc83f430538424b13298e6aa6fb143ef4d59a14946175997479dbc2d1a3cd8

_except_ for the `0x`.

I am looking for ideas/comments if I am doing everything right or may be I can improve my code.

HMAC-SHA256 Algorithm for signature calculation

I don&#39;t understand why you would need java Collections [singletonMap][1]?
Is it useful in multithreaded applications?


  [1]: http://download.oracle.com/javase/6/docs/api/java/util/Collections.html#singletonMap%28K,%20V%29

When would I use java Collections singletonMap method?

I don&#39;t completely understand how `wait` and `notify` (of `Object`) work, and as a result I&#39;m forced to slim down my attempts into the following section of code.

Main.java:

    import java.util.ArrayList;
    
    class Main
    {
      public static Main main = null;
      
      public static int numRunners = 4;
      public static ArrayList&lt;Runner&gt; runners = null;
      
      public static void main(String[] args)
      {
        main = new Main();
      }
      
      Main()
      {
        runners = new ArrayList&lt;Runner&gt;(numRunners);
        
        for (int i = 0; i &lt; numRunners; i++)
        {
          Runner r = new Runner();
          runners.add(r);
          new Thread(r).start();
        }
        
        System.out.println(&quot;Runners ready.&quot;);
        notifyAll();
      }
    }

Runner.java:

    class Runner implements Runnable
    {
      public void run()
      {
        try
        {
          Main.main.wait();
        } catch (InterruptedException e) {}
        System.out.println(&quot;Runner away!&quot;);
      }
    }

Currently I get an IllegalMonitorStateException when calling `Main.main.wait();`, but I don&#39;t understand why.  From what I can see, I need to synchronize `Runner.run`, but in doing so I assume it would only notify one thread, when the idea is to notify them all.

I&#39;ve looked at `java.util.concurrent`, but I can&#39;t find a suitable replacement (maybe I&#39;m just missing something).

Java Wait and Notify: IllegalMonitorStateException

I want to add some log.debug statements to a class I&#39;m working on, and I&#39;d like to see that in output when running the test. I&#39;d like to override the log4j properties on the command line, with something like this:

    -Dlog4j.logger.com.mypackage.Thingie=DEBUG

I do this kind of thing frequently. I am specifically only interested in a way to pass this on the command line. I know how to do it with a config file, and that doesn&#39;t suit my workflow.

How do I set log4j level on the command line?

Can anyone show me the correct way to compress and decompress tar.gzip files in java i&#39;ve been searching but the most i can find is either zip or gzip(alone). 

How to Compress/Decompress tar.gz files in java

My database of choice is MongoDB. I&#39;m writing a data-layer API to abstract implementation details from client applications - that is, I&#39;m essentially providing a single public interface (an object which acts as an IDL).

I&#39;m testing my logic as I go in a TDD manner. Before each unit test, an `@Before` method is called to create a database singleton, after which, when the test completes, an `@After` method is called to drop the database. This helps to promote independence among unit tests.

Nearly all unit tests, i.e. _performing a contextual query_, require some kind of insertion logic to occur before hand. My public interface provides an insert method - yet, it seems incorrect to use this method as precursor logic to each unit test.

Really I need some kind of mocking mechanism, yet, I haven&#39;t had much experience with mocking frameworks, and it seems that Google returns nothing re a mocking framework one might use with MongoDB.

What do others do in these situations? That is, how do people unit test code that interacts with a database?

Also, my public interface connects to a database defined in a external configuration file - it seems incorrect to use this connection for my unit testing - again, a situation that would benefit from some kind of mocking?


Unit testing with MongoDB

I need to compare two values : one a string and the other is float
so I convert the string to float then try to call `assertEquals(val1,val2)` but this is not authorized , I guess that the `assertEquals` doesn&#39;t accept float as arguments.

What is the solution for me in this case ?

JUnit assertions : make the assertion between floats

I am new to Java testing with JUnit. I have to work with Java and I would like to use unit tests.

My problem is: I have an abstract class with some abstract methods. But there are some methods which are not abstract. How can I test this class with JUnit? Example code (very simple):

    abstract class Car {

        public Car(int speed, int fuel) {
            this.speed = speed;
            this.fuel = fuel;
        }

        private int speed;
        private int fuel;
    
        abstract void drive();
    
        public int getSpeed() {
            return this.speed;
        }
    
        public int getFuel() {
            return this.fuel;
        }
    }

I want to test `getSpeed()` and `getFuel()` functions.

Similar question to this problem is [here][2], but it is not using JUnit.

In JUnit FAQ section, I found [this link][3], but I don&#39;t understand what the author want to say with this example. What does this line of code mean?

    public abstract Source getSource() ;

  [1]: http://docs.python.org/library/unittest.html
  [2]: https://stackoverflow.com/questions/3604721/how-to-test-a-method-in-an-abstract-class-with-abstract-methods
  [3]: http://c2.com/cgi/wiki?AbstractTestCases

How to test abstract class in Java with JUnit?

I have some Junit unit tests that require a large amount of heap-space to run - i.e. 1G. (They test memory-intensive functionality for a webstart app that will only run with sufficient heap-space, and will be run internally on Win 7 64-bit machines - so redesigning the tests isn&#39;t a practical suggestion.)

I am developing in Intellij IDEA, so I know I can set the JVM parameters (e.g. -Xmx1024M) for the test class. However, this is only for running the whole test class - if I want to run an individual test, I have to recreate the run congfigurations for that test method. 

Also, those are IDE and box specific - so if I switch boxes (I develop on multiple machines) or one of my colleagues tries to run the tests, those settings are not transferred. (Also, other IDEs like Eclipse and NetBeans are used by my colleagues.) FWIW, we&#39;re using mercurial for source code control.

For the build cycle, we&#39;re using Maven, so I know how to specify the JVM parameters for that.

So:
- I&#39;m looking for a way of specifying the JVM parameters that will apply for the whole test class and the individual test methods; and
- I&#39;d like to share those specification across IDEs on any machine (having picked up the code from the repository).

How to set JVM parameters for Junit Unit Tests?

I have a class which I would like to test with a public method that calls private one. I&#39;d like to assume that private method works correctly. For example, I&#39;d like something like `doReturn....when...`. I found that there is [possible solution using PowerMock](http://code.google.com/p/powermock/wiki/MockPrivate), but this solution doesn&#39;t work for me.
How It can be done? Did anybody have this problem?


Content Type	Original Author	Original Content on Stackoverflow
Question	Bohn	View Question on Stackoverflow
Solution 1 - Java	Petar Minchev	View Answer on Stackoverflow
Solution 2 - Java	punya	View Answer on Stackoverflow
Solution 3 - Java	hvgotcodes	View Answer on Stackoverflow
Solution 4 - Java	Vladi	View Answer on Stackoverflow

AssertNull should be used or AssertNotNull

Java Problem Overview

Java Solutions

Solution 1 - Java

Solution 2 - Java

Solution 3 - Java

Solution 4 - Java

Arrays.fill with multidimensional array in Java

Why is the method executed immediately when I use setTimeout?

Attributions