Use Jasmine Matchers
Learn to fuzzy match objects, strings, sets, and arrays with Jasmine's matchers. Instruct Jasmine to focus on a single test and only run and report it.
Random output function
For functions with the random
output, unit testing becomes a little bit harder. For example:
function random() {
return Math.random() > 0.5 ? 'a string' : 'another string';
}
// Unit test
it('should verify function returns a random string', () => {
expect(random()).toEqual('a string');
});
The above test fails 50% of the time as the random
function gets a Math.random
value that is anywhere between 0
and 1
. Based on that, it decides which of the two strings to return.
This is where the matcher jasmine.any
comes in. It allows toEqual
to verify that the expected
is an instance of the constructor
function that is passed in jasmine.any
. In the example above:
// Unit test
it('should verify function returns a random string', () => {
expect(random()).toEqual(jasmine.any(String));
});
That is to say, “Hey, Jasmine, make sure that the expected
is of the type String, or fail the test.”
Notice the uppercase
String
. That’s the runtime available function object String. So, typeof 'my string' === 'string'
andtypeof String('my string') === 'string'
are bothtrue
. Buttypeof new String('my string') === 'object'
. Note that the use ofnew
keyword creates an object.
Below is a unit testing example.
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