Question

In Java, create several JUnit 4 Tests for the Illegal State Exception in the following private method :


private void updateGear(int currentSpeed) {
  if (currentSpeed > 120){
    throw new IllegalStateException("Cannot be greater than 120");
  }
  if (currentSpeed <= 20) {
    currentGear = 1;
  }
  if (currentSpeed <= 40) {
    currentGear = 2;
  }
  if (currentSpeed <= 80) {
    currentGear = 3;
  }
  if (currentSpeed <= 120) {
    currentGear = 4;
  } else {
    currentGear = 5;
  }
}

Answer 1

        @Test
        void testUpdateGear() {

                try {
                        // call the updateGear method.
                        updateGear(200);
                        
                        // control should not reach below.
                        Assert.fail();
                } catch (IllegalStateException ex) {
                        // If it is IllegalStateException, then it is fine
                } catch (Exception ex) {
                        // there should not be any other exception happening in the execution
                        Assert.fail();
                }

        }

================
If your method is a private method, then you can use java reflections to test it:



      
       MyClassObject obj = new MyClassObject();
       Method method = MyGraph.class.getDeclaredMethod("updateGear", Integer.class);
       method.setAccessible(true);
method.invoke(obj, 200); // calls the method.

MyClassObject is the class name inside which the method is defined. You need to use an object of the class.

==========================

I have directly called updateGear method, but you need to put a reference of the class or object, inside which updateGear method has been defined. Let me know if any issues. Thanks!