I have an application built on typescript with decorators for some convenience property assignments and wondering how I can go about writing unit tests for them.
export function APIUrl() {
return function (target: any, key: string) {
let _value = target[key];
function getter() {
return _value;
}
function setter(newValue) {
_value = getApiURL();
}
if (delete target[key]) {
Object.defineProperty(target, key, {
get: getter,
set: setter
});
}
};
}
In a spec class I have,
it("should return url string", ()=> {
@APIUrl();
let baseURL:string;
expect(baseURL typeOf string).toBe(true)
})
Decorators provide a way to add both annotations and a meta-programming syntax for class declarations and members. Decorators are a stage 2 proposal for JavaScript and are available as an experimental feature of TypeScript. NOTE Decorators are an experimental feature that may change in future releases.
For TypeScript, unit tests are run against the generated JavaScript code. In most TypeScript scenarios, you can debug a unit test by setting a breakpoint in TypeScript code, right-clicking a test in Test Explorer, and choosing Debug.
Let's try to approach writing a test case for decorator as if we were writing test for regular function: we need to call using_email_address with certain input and assert that whatever happens inside of it produces expected output/result. This technique of writing tests is called “black box testing”.
Since decorators are just functions I would suggest to just test them like any other function. And only if you really need to, add one tests that shows how to use the decorator with a class/member/...
Here is an example such a test could look like:
import test from 'ava';
import { APIUrl } from './path';
const decorate = new APIUrl();
test.before(t => {
let obj = { someProp: 'foo' };
decorate(obj, 'someProp');
t.context.foo = obj;
});
test('should return original value', t => {
t.is(t.context.foo.someProp, 'foo');
});
Another approach could be to setup some properties and/or methods that use your decorators and test their usage directly.
Note: decorators can only be used on class methods and members so you'd need to create a dummy class in your test.
Here's an example:
//Test Setup
class Test {
@APIUrl()
url: string;
@AnotherDecorator()
anotherFunction() {}
}
//Unit tests
describe('Decorator Tests', () => {
it('should work', () => {
const t = new Test();
expect(t.url).toEqual("something");
expect(t.anotherFunction()).toReturn("something else");
});
}
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