Using coverage reports for better tests

January 26, 2008 – 2:34 pm

After creating a Cobertura Plugin for Grails, I thought I’d give it a test run on some simple domain class logic and tests. Consider this example in grails-app/domain:

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class State {
	String name
	String postalCode
 
	def isMinnesota(){
		return 'MN' == postalCode
	}
 
	def isWisconsin(){
		return 'WI' == postalCode
	}
}

The two helper methods (isMinnesota and isWisconsin) deserve some tests:

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void testIsMinnesota() {
	state.postalCode = 'MN'
	assertTrue('should be true when state is MN', state.isMinnesota())
}
 
void testIsWisconsin() {
	state.postalCode = 'WI'
	assertTrue('should be true when state is WI', state.isWisconsin())
}

Looks good, right? When I run grails test-app-coverage and look at the reports, there is 100% line coverage, but the branch coverage is only 50%:

The tests didn’t take into account the case in which the state is NOT Minnesota or NOT Wisconsin. Just modify the test cases to add some assertions:

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void testIsMinnesota() {
	state.postalCode = 'NOT mn'
	assertFalse('should be false when state is not MN', state.isMinnesota())
	state.postalCode = 'MN'
	assertTrue('should be true when state is MN', state.isMinnesota())
}
 
void testIsWisconsin() {
	state.postalCode = 'NOT wi'
	assertFalse('should be false when state is not WI', state.isWisconsin())
	state.postalCode = 'WI'
	assertTrue('should be true when state is WI', state.isWisconsin())
}

And run the reports again:

And now there’s 100% line coverage AND 100% branch coverage – perfect.

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