Testing can be performed at different levels.
Testing Pyramid illustrates the relationship between the number of tests and the effort required to create them.
Unit Tests are the simplest and most numerous. They are usually written by developers while implementing a feature (details).
The Goal of Unit Testing is to verify the correctness of modules (functions, classes) in isolation and to catch defects early in development.
Let’s act as a developer and write a function that adds two integers sum.
We’ll use pseudocode during development — informal code that is easier to read and understand.
sum(a, b) {
declare a variable c
perform addition a + b
store the sum in a variable c
return the variable c
}Pseudocode
public int sum(int a, int b) {
int c;
c = a + b;
return c;
}
Java code
A unit test defines the expected and actual results of a function execution.
If the expected and actual results match, the test passes PASS, otherwise, the test fails FAIL.
int expected = 3; //expected result
int actual = sum(1, 2); //actual result
expected == actual;
PASS
== equals sign
int expected = 2147483648;
int actual = sum(2147483646, 2);
expected != actual;
FAIL
!= not equals sign
Food for thought: Integer overflow
The completeness of testing is measured using code coverage. However, 100% coverage does not guarantee the absence of bugs. It only shows which parts of the code are actually executed during a test run.
In the figure, line 9 is highlighted in red because it was not covered by a test. In other words, the function
sum
was never called with arguments a and b whose sum would satisfy the condition on line 8.
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