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    Interface Expect

    The expect function is used every time you want to test a value. You will rarely call expect by itself.

    interface Expect {
        not: InverseAsymmetricMatchers;
        addSnapshotSerializer(serializer: Plugin_2): void;
        any(classType: any): any;
        anything(): any;
        arrayContaining<E = any>(arr: readonly E[]): any;
        assertions(num: number): void;
        closeTo(num: number, numDigits?: number): any;
        extend(obj: ExpectExtendMap): void;
        getState(): MatcherState & Record<string, any>;
        hasAssertions(): void;
        objectContaining<E = {}>(obj: E): any;
        setState(state: object): void;
        stringContaining(str: string): any;
        stringMatching(str: string | RegExp): any;
        <T = any>(actual: T): JestMatchers<T>;
    }

    • The expect function is used every time you want to test a value. You will rarely call expect by itself.

      Type Parameters

      • T = any

      Parameters

      • actual: T

        The value to apply matchers against.

      Returns JestMatchers<T>

    Index

    Properties

    not

    Methods

    addSnapshotSerializer any anything arrayContaining assertions closeTo extend getState hasAssertions objectContaining setState stringContaining stringMatching

    Properties

    not: InverseAsymmetricMatchers

    Methods

    • Adds a module to format application-specific data structures for serialization.

      Parameters

      • serializer: Plugin_2

      Returns void

    • Matches anything that was created with the given constructor. You can use it inside toEqual or toBeCalledWith instead of a literal value.

      Parameters

      • classType: any

      Returns any

      function randocall(fn) {
        return fn(Math.floor(Math.random() * 6 + 1));
      }

      test('randocall calls its callback with a number', () => {
        const mock = jest.fn();
        randocall(mock);
        expect(mock).toBeCalledWith(expect.any(Number));
      });

    • Matches anything but null or undefined. You can use it inside toEqual or toBeCalledWith instead of a literal value. For example, if you want to check that a mock function is called with a non-null argument:

      Returns any

      test('map calls its argument with a non-null argument', () => {
        const mock = jest.fn();
        [1].map(x => mock(x));
        expect(mock).toBeCalledWith(expect.anything());
      });

    • Matches any array made up entirely of elements in the provided array. You can use it inside toEqual or toBeCalledWith instead of a literal value.

      Optionally, you can provide a type for the elements via a generic.

      Type Parameters

      • E = any

      Parameters

      • arr: readonly E[]

      Returns any

    • Verifies that a certain number of assertions are called during a test. This is often useful when testing asynchronous code, in order to make sure that assertions in a callback actually got called.

      Parameters

      • num: number

      Returns void

    • Useful when comparing floating point numbers in object properties or array item. If you need to compare a number, use .toBeCloseTo instead.

      The optional numDigits argument limits the number of digits to check after the decimal point. For the default value 2, the test criterion is Math.abs(expected - received) < 0.005 (that is, 10 ** -2 / 2).

      Parameters

      • num: number
      • OptionalnumDigits: number

      Returns any

    • You can use expect.extend to add your own matchers to Jest.

      Parameters

      Returns void

    • Returns MatcherState & Record<string, any>

    • Verifies that at least one assertion is called during a test. This is often useful when testing asynchronous code, in order to make sure that assertions in a callback actually got called.

      Returns void

    • Matches any object that recursively matches the provided keys. This is often handy in conjunction with other asymmetric matchers.

      Optionally, you can provide a type for the object via a generic. This ensures that the object contains the desired structure.

      Type Parameters

      • E = {}

      Parameters

      • obj: E

      Returns any

    • Parameters

      • state: object

      Returns void

    • Matches any received string that contains the exact expected string

      Parameters

      • str: string

      Returns any

    • Matches any string that contains the exact provided string

      Parameters

      • str: string | RegExp

      Returns any

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