THE SITUATION:
Hello guys. I am learning jasmine to test my angular app.
I have create a basic function that does multiply two numbers. If the parameters given are not a number, the function throw an error.
I then made two very basic tests.
The first to check if the function properly multiply the numbers. The second to check if the function properly throw an error if a string is given as parameter.
The first test pass, the second not. And i don't understand why.
THE CODE:
The function:
function Multiply( num1, num2 )
{
var result;
if (isNaN(num1) || isNaN(num2))
{
throw new Error("not a number");
}
else
{
result = num1 * num2;
return result;
}
}
The spec:
describe('The function', function ()
{
it('properly multiply two numbers', function ()
{
result = Multiply(10, 5);
expect(result).toEqual(50);
});
it('throw an error if a parameter is not a number', function ()
{
result = Multiply(10, 'aaaa');
expect(result).toThrow(new Error("not a number"));
});
});
THE OUTPUT:
2 specs, 1 failure
Spec List | Failures
The function throw an error if a parameter is not a number
Error: not a number
Error: not a number
at Multiply (http://localhost/jasmine_test/src/app.js:8:9)
If i understand properly Jasmine. Both test should pass, because in the second case the function throw the error as we expected.
THE QUESTION:
How can i test if a function properly throw an error?
EDIT:
I am trying this new code, but is still not working:
describe('The function', function ()
{
it('throw an error if a parameter is not a number', function ()
{
expect(function() { Multiply(10, 'aaaa') }).toThrowError(new Error("not a number"));
});
});
OUTPUT:
2 specs, 1 failure
Spec List | Failures
The function throw an error if a parameter is not a number
Error: Expected is not an Error, string, or RegExp.
THE SITUATION:
Hello guys. I am learning jasmine to test my angular app.
I have create a basic function that does multiply two numbers. If the parameters given are not a number, the function throw an error.
I then made two very basic tests.
The first to check if the function properly multiply the numbers. The second to check if the function properly throw an error if a string is given as parameter.
The first test pass, the second not. And i don't understand why.
THE CODE:
The function:
function Multiply( num1, num2 )
{
var result;
if (isNaN(num1) || isNaN(num2))
{
throw new Error("not a number");
}
else
{
result = num1 * num2;
return result;
}
}
The spec:
describe('The function', function ()
{
it('properly multiply two numbers', function ()
{
result = Multiply(10, 5);
expect(result).toEqual(50);
});
it('throw an error if a parameter is not a number', function ()
{
result = Multiply(10, 'aaaa');
expect(result).toThrow(new Error("not a number"));
});
});
THE OUTPUT:
2 specs, 1 failure
Spec List | Failures
The function throw an error if a parameter is not a number
Error: not a number
Error: not a number
at Multiply (http://localhost/jasmine_test/src/app.js:8:9)
If i understand properly Jasmine. Both test should pass, because in the second case the function throw the error as we expected.
THE QUESTION:
How can i test if a function properly throw an error?
EDIT:
I am trying this new code, but is still not working:
describe('The function', function ()
{
it('throw an error if a parameter is not a number', function ()
{
expect(function() { Multiply(10, 'aaaa') }).toThrowError(new Error("not a number"));
});
});
OUTPUT:
2 specs, 1 failure
Spec List | Failures
The function throw an error if a parameter is not a number
Error: Expected is not an Error, string, or RegExp.
-
You need to run it in an anonymous function passed as "expect" argument.
expect(function() { Multiply(10, 'aaaa') })- otherwise jasmine doesn't have chance to capture it – zerkms Commented Jan 10, 2015 at 11:59 -
you would need
.toThrowError(Error, "not a number"). Updated my answer. – lonelyelk Commented Nov 23, 2016 at 10:22
3 Answers
Reset to default 7If I understand correctly you need to pass a function into the expect(...) call.
The code you have here:
expect(result).toThrow(new Error("not a number"));
Is checking the result of Multiply, which when it works is fine, but like I said .toThrow() expects a function, I'd use an anonymous function instead, see below:
expect( function(){ Multiply(10, 'aaaa'); } ).toThrow(new Error("not a number"));
EDIT: Did a quick search and this blog post is a very detailed explanation of what I am trying to say.
You need to put the code you expect to throw an error into a function:
expect(function () {
Multiply(10, 'aaaa');
}).toThrow(Error, 'not a number');
Otherwise, when you run your assertions, the error has already been thrown outside the scope. You can see available syntax for error matching in jasmine docs
- The above methods are exactly true for exceptions handled inside the methods.
- When you've to test the services you can use
mocking mechanismto do that. Use the advantage of NgModule providers section to create the mocks.
In describe() block,
providers: [{ provide: APIService, useValue: { api: { filterTaskDetails: () => throwError('Error') }}}]
throwErrorto be imported fromrxjs.
- In expect() block test it as,
spyOn(ponent['toaster'], 'showError');
/** add respected it() blocks**/
expect(ponent['toaster'].showError).toHaveBeenCalledTimes(1);