How to test Typescript class members in React with Jest

Question

I have a Typescript class (with react) with public and private member functions.

export class Myclass {
    private itemList: SomeItem[];

    constructor(params) {

    }

    public method1() {

    }

    private method2() {

    }
}

How can I test method1 and method2 in my code using jest. I can do it for functions who are exported and are not members of a class. But how can I do it for class members.

public method should be available to you upon initiation in your test — Rikin
– Rikin, Commented Aug 23, 2019 at 17:17

caseyWebb · Accepted Answer · 2019-08-23 18:41:47Z

1

First, you need an instance...

const instance = new MyClass()

Then, you can test method1 by calling it directly...

expect(instance.method1()).toBe(...)

For method2, you've got 3 options...

Use @ts-ignore:

// @ts-ignore
expect(instance.method2()).toBe(...)

Cast as any:

expect((instance as any).method2()).toBe(...)

// no type safety on method2

Change to protected and extend:

class MyClass {
  protected method2() {}
}

class MyClassTester extends MyClass {
  public runTests() {
    expect(this.method2()).toBe(...)
  }

  // OR

  public method2Accessor(...args: any[]) {
    return this.method2(...args)
  }
}

const instance = new MyClassTester()

instance.runTests()

// OR

expect(instance.method2Accessor()).toBe(...)

// fully type-safe

answered Aug 23, 2019 at 18:41

caseyWebb

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Comments

user6269864 · Accepted Answer · 2019-08-23 17:22:06Z

0

You have to create an instance of the class and then call its public methods in your test. There is no way around it.

answered Aug 23, 2019 at 17:22

user6269864

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