Q-back/teststate

Create immutable test state reinitialized after each test case with type inference

teststate

Create immutable test state reinitialized after each test case with type inference.

Install

Using npm

npm install teststate

Using yarn

yarn add --dev teststate

How to use this library?

// (1) import testState method from teststate module.
import { testState } from "teststate";

const EXPECTED_VALUE = "...";

describe("test fooMethod", () =>
  // (2) Declare state, pass a callback that builds state to be recreated between each tests.
  const state = testState(() => {
    const foo = fooFactory();
    return { foo };
  }, beforeEach);

  it("returns bar", () => {
    // (3) Use state inside test methods.
    const result = fooMethod(state.foo);

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

Why should I use this library?

Normally, when you define some state in beforeEach hook, you do:

describe("tests", () => {
  let foo: null | SomeType = null;

  beforeEach(() => {
    foo = createSomeTypeInstance();
  });

  it("passes the test", () => {
    // here foo can be SomeType | null
  });
});

describe("tests", () => {
  const state = testState(() => {
    return {
      foo: createSomeTypeInstance(),
    };
  }, beforeEach);

  it("passes the test", () => {
    // here state.foo must be SomeType
  });
});

With teststate, foo is always of type SomeType and can be accessed via state.foo.