How to write a Unit Test?

Question

I have a Java class. How can I unit test it?

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In my case, I have class does a binary sum. It takes two byte[] arrays, sums them, and returns a new binary array.

Answer 1

1. Define the expected and desired output for a normal case, with correct input.

2. Now, implement the test by declaring a class, name it anything (Usually something like TestAddingModule), and add the testAdd method to it (i.e. like the one below) :

   • Write a method, and above it add the @Test annotation.
   • In the method, run your binary sum and assertEquals(expectedVal,calculatedVal).

   • Test your method by running it (in Eclipse, right click, select Run as → JUnit test).

     //for normal addition 
     @Test
     public void testAdd1Plus1() 
     {
         int x  = 1 ; int y = 1;
         assertEquals(2, myClass.add(x,y));
     }
     

3. Add other cases as desired.

   • Test that your binary sum does not throw a unexpected exception if there is an integer overflow.

   • Test that your method handles Null inputs gracefully (example below).

     //if you are using 0 as default for null, make sure your class works in that case.
     @Test
     public void testAdd1Plus1() 
     {
         int y = 1;
         assertEquals(0, myClass.add(null,y));
     }