Transcript Testing

Testing code
COMP204
How to?
• “manual”
– Tedious, error-prone, not repeatable
• “automated” by writing code:
– Assertions
– Junit
Assertions
• “manually”
if (! check()) {
throw new RuntimeException(“…”);
}
• Better: use “assert” command
assert check();
Will only be checked if enabled: -ea
assert check42(a) : “check42 failed for “ + a ;
Assertions continued
• Use in methods to check preconditions:
assert (parameter1 != null);
• Or post-conditions before returning:
assert (stack.size() == oldSize+1);
• Or class-invariants at the start and end
of public methods:
assert integrity();
Junit
• Unit testing implements tests for “units”
in separate classes that usually mirror
the original class structure:
– BoundedStack.java
– BoundedStackTest.java
• www.junit.org
Unit tests
• Check all public methods
• Can even be used as specifiation (e.g.
in TDD - test driven development),
written *before* the code they test
• Run after a every code change
• Have someone else write unit tests
Junit
• import static org.junit.Assert.*;
• assertEquals(a,b); assertArrayEquals(x,y); …
• Annotations:
–
–
–
–
–
–
@Test
@Before
@After
@Ignore
@Test(expected = RuntimeException.class)
@Test(timeout = 100)
How good are the tests
• Code coverage:
– Is every line executed at least once?
– Borderline cases (e.g. +/- 1)
public int sumAndSort(Integer[] a) {
int sum = 0;
for(Integer e: a) sum += e;
Arrays.sort(a);
return sum;
}
Two different “full cover” tests
public void someTest() {
assertEquals(6, sumAndSort(new Integer[]{3,1,2}));
}
public void betterTest() {
Integer[] a = new Integer[]{3,1,2};
assertEquals(6, sumAndSort(a));
assertArrayEquals(new Integer[]{1,2,3}, a);
}
Jumble: mutation testing
• Open source, Honour’s project of Tin
Pavlinic, supervised by Prof.John
Cleary (ReelTwo), a few years ago
• Mutates the byte-code of a class, then
checks whether the unit-tests pick up
the changes