Unit testing allows us to check - by running other code - that each method of our code, individually, works correctly. Of course, it doesn’t guarantee that the the methods interact correctly or not.
Unit testing is based on the fundamental assumption that for a given input, there is an expected output. Creating a list of such input-output mappings, we can determine if the method, in fact, works correctly.
Conside a method supposed to return the highest of three numbers. An input-output mapping for such a method is listed below.
| Input | Output |
|---|---|
| 5, 7, 9 | 9 |
| 1, 10, 100 | 100 |
| 0, 0, 0 | 0 |
Is the above set of mappings sufficient?
No, in all cases, the third value is the answer. A function that simply returns the third value will pass this insufficient test
A more comprehensive set of mappings is provided below.
| Input | Output |
|---|---|
| 5, 7, 9 | 9 |
| 100, 1, 10 | 100 |
| 0, 8, 0 | 8 |
| -5, -100, -1 | -1 |
| -9, -9, 0 | 0 |
| 6, 6, 6 | 6 |
Write a set of input-output mappings for a function that when passed an integer, returns true if all the digits in the integer are even (0/2/4/6/8), and false otherwise.
| Input | Output | |————|——–| | 284666604 | true | | 284661604 | false | | 148 | false | | 227 | false | | -2486 | true | | -9486 | false | | 0 | true |
Write a set of input-output mappings for a function that when passed an integer array, returns true if the array is in ascending order (for each item of thearray, the item is less than or equal to the next item (if any)), and false otherwise.
| Input | Output | |————|——–| | {5, 8, 12, 100} | true | | {6, 6, 6} | true | | {20} | true | | {} | true | | null | not well-defined | | {5, 8, 12, 11} | false | | {6, 4, 4, 8} | false |
Write a set of input-output mappings for a function that when passed an integer array, returns true if each item of the array occurs exactly once, and false otherwise. Return false if the array is null.
| Input | Output | |————|——–| | {5, 8, 12, 100} | true | | {6, 6, 6} | false | | {20} | true | | {} | true | | null | false | | {2, 7, 1, 9, 3, -5, -5} | false | | {2, -5, 7, 1, 9, 3, -5} | false |
JUnit is a unit testing framework for Java. It operates using assertions to determine if a particular test passes or not.
A list of important assertions are given below:
assertTrue(boolean expression): passes if the boolean expression passed to the assertion is true, fails otherwise.
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assertTrue(5 > 3): pass
assertTrue(6 == 12/3): fail
assertFalse(boolean expression): passes if the boolean expression passed to the assertion is false, fails otherwise.
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assertFalse(2 >= 3): pass
assertFalse(6 == 12/2): fail
assertEquals(expected integer value, integer expression): passes if the integer expression passed to the assertion equals the expected integer value, fails otherwise.
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assertEquals(5, 10/2): pass
assertEquals(5, 2*3): fail
assertEquals(expected floating-point value, floating-point expression, tolerance): passes if the floating-point expression passed to the assertion is within tolerance distance of the expected floating-point value, fails otherwise.
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assertEquals(1.2, 1.21, 0.02): pass
assertEquals(1.2, 1.23, 0.02): fail
assertNull(reference): passes if the reference (object/array) passed to the assertion is null, fails otherwise.
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assertNull(null): pass
assertNull(new int[]{1,7,2,9}): fail
assertNotNull(reference): passes if the reference (object/array) passed to the assertion is not null, fails otherwise.
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assertNotNull(new int[]{1,7,2,9}): pass
assertNotNull(null): fail
assertArrayEquals(expected integer array, actual integer array): passes if the actual integer array passed to the assertion equals the expected integer array, fails otherwise.
Assuming three arrays created as following:
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int[] a = {1,7,2,9};
int[] b = {1,7,2};
int[] c = {1,7,2,9};
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assertArrayEquals(a,c): pass
assertArrayEquals(a,b): fail
First you need a method that you need to test.
Let’s take a look at the following code that contains a single method sumEven.
The JUnit test is a separate class created to test this method. The following video describes the steps to create a JUnit test. Generally a test is written before implementing a method.