Static Methods

Version: 5.2.1

Static Methods

The first example of using the tester library: testing static methods:

At times students first learn ot program simple static methods that typically perform some mathematical calculations. For examples, we may define the following methods for shapes:

// methods that compute some information about shapes
class ShapeMethods{

  // compute the perimeter of a rectangle of the given width and height
  static int rectPerimeter(int width, int height){
    return 2 * width + height;
  }

  // compute the area of a rectangle of the given width and height
  static int rectArea(int width, int height){
    return width * height;
  }

  // compute the perimeter of a circle of the given radius
  static double circlePerimeter(int radius){
    return 2 * Math.PI * radius;
  }

  // compute the area of the circle of the given radius
  static double circleArea(int radius){
    return Math.PI * radius * radius;
  }
}

We first test the methods for rectangles as follows:

class ExamplesShapesMethods{
  ExamplesShapesMethods(){}

  // test the methods for rectangles
  void testRectMethods(Tester t){
    t.checkExpect(ShapeMethods.rectArea(20, 40), 800);
    t.checkExpect(ShapeMethods.rectArea(30, 10), 300);
    t.checkExpect(ShapeMethods.rectPerimeter(20, 40), 120);
    t.checkExpect(ShapeMethods.rectPerimeter(30, 10), 80);
  }
}

and get the following results:

Tester Prima v.1.5.1 - 17 June 2012
-----------------------------------
Tests defined in the class: ExamplesShapesMethods:
---------------------------
ExamplesShapesMethods:
---------------

new ExamplesShapesMethods:1()
---------------

Ran 4 tests.
2 tests failed.

Full test results:
-------------------

Success in the test number 1

actual:                                 expected:
800                                               800

Success in the test number 2

actual:                                 expected:
300                                               300

Error in test number 3

tester.ErrorReport: Error trace:
        at ExamplesShapesMethods.testRectMethods(ShapesMethods.java:33)
        at ExamplesShapesMethods.main(ShapesMethods.java:40)
actual:                                 expected:
80................................................120

Error in test number 4

tester.ErrorReport: Error trace:
        at ExamplesShapesMethods.testRectMethods(ShapesMethods.java:34)
        at ExamplesShapesMethods.main(ShapesMethods.java:40)
actual:                                 expected:
70................................................80

--- END OF FULL TEST RESULTS ---

We see that even in this simple example we can make a silly error that will haunt us later on, if not detected.

We fix the problem and add the tests for the circle methods:

// test the methods for circle
void testCircleMethods(Tester t){
  t.checkExpect(ShapeMethods.circleArea(10), 314.15926);
  t.checkExpect(ShapeMethods.circleArea(20), 1256.63704);
  t.checkExpect(ShapeMethods.circlePerimeter(10), 62.831852);
  t.checkExpect(ShapeMethods.circlePerimeter(20), 125.663704);
}

but when we run the tests we see that all four test failed:

Error in test number 5

tester.ErrorReport: Error trace:
        at ExamplesShapesMethods.testCircleMethods(ShapesMethods.java:39)
        at ExamplesShapesMethods.main(ShapesMethods.java:48)
The comparison involved inexact numbers with relative tolerance 0.0010
actual:                                 expected:
314.1592653589793.................................314.15926

Error in test number 6

tester.ErrorReport: Error trace:
        at ExamplesShapesMethods.testCircleMethods(ShapesMethods.java:40)
        at ExamplesShapesMethods.main(ShapesMethods.java:48)
The comparison involved inexact numbers with relative tolerance 0.0010
actual:                                 expected:
1256.6370614359173................................1256.63704

Error in test number 7

tester.ErrorReport: Error trace:
        at ExamplesShapesMethods.testCircleMethods(ShapesMethods.java:41)
        at ExamplesShapesMethods.main(ShapesMethods.java:48)
The comparison involved inexact numbers with relative tolerance 0.0010
actual:                                 expected:
62.83185307179586.................................62.831852

Error in test number 8

tester.ErrorReport: Error trace:
        at ExamplesShapesMethods.testCircleMethods(ShapesMethods.java:42)
        at ExamplesShapesMethods.main(ShapesMethods.java:48)
The comparison involved inexact numbers with relative tolerance 0.0010
actual:                                 expected:
125.66370614359172................................125.663704

The tester library informs us that these tests involved inexact comparisons. So, we need to change the methods that perform the test comparison to checkInexact as follows:

// test the methods for circle
void testCircleMethods(Tester t){
  t.checkInexact(ShapeMethods.circleArea(10), 314.15926, 0.01);
  t.checkInexact(ShapeMethods.circleArea(20), 1256.63704, 0.01);
  t.checkInexact(ShapeMethods.circlePerimeter(10), 62.831852, 0.01);
  t.checkInexact(ShapeMethods.circlePerimeter(20), 125.663704, 0.01);
}

Now all test pass, but we still will get the inexact warning, as the equality of inexact values is not transitive, and so should not be considered a true equality:

Tester Prima v.1.5.1 - 17 June 2012
-----------------------------------
Tests defined in the class: ExamplesShapesMethods:
---------------------------
ExamplesShapesMethods:
---------------

new ExamplesShapesMethods:1()
---------------

Ran 8 tests.
All tests passed.
Issued 4 warnings of inexact comparison.

Full test results:
-------------------
...

Success in the test number 5

The comparison involved inexact numbers with relative tolerance 0.01
actual:                                 expected:
314.1592653589793.................................314.15926

Success in the test number 6

The comparison involved inexact numbers with relative tolerance 0.01
actual:                                 expected:
1256.6370614359173................................1256.63704

Success in the test number 7

The comparison involved inexact numbers with relative tolerance 0.01
actual:                                 expected:
62.83185307179586.................................62.831852

Success in the test number 8

The comparison involved inexact numbers with relative tolerance 0.01
actual:                                 expected:
125.66370614359172................................125.663704

--- END OF FULL TEST RESULTS ---

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