spying_and_stubbing_interactions_with_ts-mockito.md

Tools

• Jest
• Expect - Jest
• ts-mockito

Example of spying an interaction

interface Collaborator {
    collaborate(): void;
}

class MyClass {
    private collaborator: Collaborator;
    
    constructor(collaborator: Collaborator) {
        this.collaborator = collaborator;
    }

    run(): void {
        this.collaborator.collaborate();
    }
}

test('example of a spying an interaction', () => {
    const collaborator = mock<Collaborator>();
    const myClass = new MyClass(instance(collaborator));

    myClass.run();

    verify(collaborator.collaborate()).once();
});

Example of stubbing an interaction

interface Collaborator {
    collaborate(): string;
}

class MyClass {
    private collaborator: Collaborator;
    
    constructor(collaborator: Collaborator) {
        this.collaborator = collaborator;
    }

    run(): void {
        return this.collaborator.collaborate();
    }
}

test('example of a stubbing an interaction', () => {
    const collaboratorResponse = "some response";
    const collaborator = mock<Collaborator>();
    when(collaborator.collaborate()).thenReturn(collaboratorResponse);
    const myClass = new MyClass(instance(collaborator));

    const result = myClass.run();

    expect(result).toBe(collaboratorResponse);
});