What are the best practices for testing a class function that executes a mongoose query?

Question

What are the best practices for testing a class function that executes a mongoose query?

Within my class, there are multiple class functions, with one specifically executing a mongoose query. The structure is similar to:

export class ExampleService {
  constructor(
    @InjectModel(Example.name) private exampleModel: Model<Example>,
    @InjectModel(MyMongoose.name) private myMongooseModel: Model <MyMongoose>
  ){}

  //function in focus for unit testing
  async addToCollection(name) {
    if(name.length < 1) throw new Error ('No name entered')
    else {
      this.myMongooseModel.query()
    }
  }

  //..other functions that utilize addToCollection()

}

My goal is to test the behavior of addToCollection() by ensuring it throws an error when name is too short, and that it initiates a query to myMongooseModel when the name is sufficient.

Past attempts at mocking ExampleService led to having to mock not only addToCollection but also the query to myMongooseModel. This approach seems incorrect for testing this specific function. How can I solely mock the call to myMongooseModel?

typescript unit-testing jestjs

Answer 1

Answer №1

myMongooseModel is an essential dependency that can be easily mocked by creating a spy object and injecting it into the ExampleService.

For example:

describe("ExampleService", () => {
  let service: ExampleService;

  let exampleModelMock;
  let myMongooseModelMock;

  let logSpy;

  beforeEach(() => {
    logSpy = jest.spyOn(console, 'log'); // spying on the log function
    exampleModelMock = {}; // mocking the example model
    myMongooseModelMock = {
      query: jest.fn(), // mocking the query function
    };

    service = new ExampleService(exampleModelMock, myMongooseModelMock); // injecting dependencies
  });

  it("should NOT call query when name is too short", async () => {
    await service.addToCollection("");

    expect(logSpy).toHaveBeenCalledWith('no name entered');
    expect(myMongooseModelMock.query).not.toHaveBeenCalled();
  });

  it("should call query when name is NOT too short", async () => {
    await service.addToCollection("long_name");

    expect(logSpy).not.toHaveBeenCalled();
    expect(myMongooseModelMock.query).toHaveBeenCalled();
  });
});

Answer 2

myMongooseModel is an essential dependency that can be easily mocked by creating a spy object and injecting it into the ExampleService.

For example:

describe("ExampleService", () => {
  let service: ExampleService;

  let exampleModelMock;
  let myMongooseModelMock;

  let logSpy;

  beforeEach(() => {
    logSpy = jest.spyOn(console, 'log'); // spying on the log function
    exampleModelMock = {}; // mocking the example model
    myMongooseModelMock = {
      query: jest.fn(), // mocking the query function
    };

    service = new ExampleService(exampleModelMock, myMongooseModelMock); // injecting dependencies
  });

  it("should NOT call query when name is too short", async () => {
    await service.addToCollection("");

    expect(logSpy).toHaveBeenCalledWith('no name entered');
    expect(myMongooseModelMock.query).not.toHaveBeenCalled();
  });

  it("should call query when name is NOT too short", async () => {
    await service.addToCollection("long_name");

    expect(logSpy).not.toHaveBeenCalled();
    expect(myMongooseModelMock.query).toHaveBeenCalled();
  });
});

What are the best practices for testing a class function that executes a mongoose query?

Answer №1

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