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In this tutorial, You learned how to test a mock interface in typescript.
Typescript is advanced to javascript with strong features like typesafe checking.
Jest is a unit testing framework like jasmine from Facebook.
How to mock an interface in Jest?
Let’s declare an interface in typescript with an enum being used in the interface.
role.ts:
enum ROLE {
ADMIN,
SALES,
FINANCE
}
user.ts:
export interface User {
id: number;
name: string;
role: ROLE.ADMIN | ROLE.FINANCE | ROLE.SALES;
}
Here is an User.spec.ts for the Jest mock interface example.
- First create a mock interface with all defined values
- Check for mock object undefined and values asserted for expected
describe('User', () => {
const mock = jest.fn<User, []>(() => {
return {
id: 1,
name: 'john',
role: ROLE.ADMIN,
};
});
it('should check mock object', () => {
const user = mock();
expect(user).toBeDefined();
});
it('should check properties', () => {
const user = mock();
expect(user.name).toEqual('john');
expect(user.role).toEqual(ROLE.ADMIN);
});
});
How do you mock an interface that contains an async promise
Let’s define a service with the following method returns Promise.
interface UserService {
getEmployee: () => Promise<any>
}
Here is an example of the jest async method interface example.
Here are steps for creating mock
- First, create a mock interface using jest. fn with a method resolving to an object
- Next assert check for the mock object is defined
- check to assert object promise method to check resolved value
let userServiceMock: UserService;
describe('UserService', () => {
beforeAll(() => {
userServiceMock.getEmployee = jest.fn(() => Promise.resolve({
id: 1,
name: 'john',
role: ROLE.ADMIN,
}));
});
it('should check mock object', () => {
expect(userServiceMock).toBeDefined();
});
it('should check properties', () => {
userServiceMock.getEmployee();
expect(userServiceMock.getEmployee).toHaveBeenCalled();
expect(userServiceMock.getEmployee.mock.results[0].value).resolves.toBe({
id: 1,
name: 'john',
role: ROLE.ADMIN,
})
});
});
Conclusion
You learned to mock an interface in typescript with jest framework and also mock an interface with the async method.
