CODEWITHSUNDEEP
typescriptjestjsts-jest
Charlie Bamford
Charlie Bamford

Reputation: 1309

Factory class creates untyped objects

I have a factory. It's purpose is to facilitate dependency injection. It looks something like:

import SomeImportantObject from "./SomeImportantObject"
import DataInterface from "./DataInterface"

class NoodleFactory {
  this.dependency: SomeImportantObject
  constructor(dependency: SomeImportantObject) {
    // Dependencies.
    this.dependency = dependency;
  }

  create(data: DataInterface) {
    return new Noodle(data, this.dependency);
  }
}

I was creating a test for it to ensure that it is correctly creating objects. The test is very similar to:

data = {
  // Data.
}

mockDependency = "a mocked dependency."

testNoodleFactory = new NoodleFactory(mockDependency);

const expected = new Noodle(data, mockDependency);
const actual = testNoodleFactory.create(data);

test("Factory creates noodles", () => {
  expect(actual).toMatchObject(expected);
});

When I run the test, I get the following error:

    @@ -1,6 +1,6 @@
    - Noodle {
    + Object {

All internal data matches.

What is causing the object types to be different?

Upvotes: 0

Views: 46

Answers (1)

Josh Wulf
Josh Wulf

Reputation: 4877

Use console.log to inspect what gets returned from each call.

Reasoning about your code (without executing it), I can see no explanation for this.

I had a quick look over the Jest source code. The object matcher is here: https://github.com/facebook/jest/blob/master/packages/expect/src/matchers.ts#L878

It uses the iterableEquality and subsetEquality tests from here: https://github.com/facebook/jest/blob/master/packages/expect/src/utils.ts

toMatchObject checks that it is an object, that they have the same constructor (that looks like the failing test), and then that the object you compare it with has a subset of the keys of the object you are testing.

I would look at the constructor of the object returned from the Noodle factory in the first instance.

If you create an MRE in a GitHub repo, I'll check it out and trace the code execution (or you could do that - just inject console.log statements in the Jest in the node_modules).

Upvotes: 1

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