Function stub

testing/mock.ts:1055–1151

(
  self: Self,
  property: keyof Self,
  func?: (this: Self, ...args: Args) => Return,
)

  ) => GetReturnFromProp<Self, Prop>,
): Stub<Self, GetParametersFromProp<Self, Prop>, GetReturnFromProp<Self, Prop>>;
export function stub<
  Self,
  Args extends unknown[],
  Return,
>(
  self: Self,
  property: keyof Self,
  func?: (this: Self, ...args: Args) => Return,
): Stub<Self, Args, Return> {
  if (self[property] !== undefined && typeof self[property] !== "function") {
    throw new MockError(
      "Cannot stub: property is not an instance method",
    );
  }
  if (isSpy(self[property])) {
    throw new MockError(
      "Cannot stub: already spying on instance method",
    );
  }

  const propertyDescriptor = Object.getOwnPropertyDescriptor(self, property);
  if (propertyDescriptor && !propertyDescriptor.configurable) {
    throw new MockError("Cannot stub: non-configurable instance method");
  }

  const fake = func ?? (() => {}) as (this: Self, ...args: Args) => Return;

  const original = self[property] as unknown as (
    this: Self,
    ...args: Args
  ) => Return;
  const calls: SpyCall<Self, Args, Return>[] = [];
  let restored = false;
  const stub = function (this: Self, ...args: Args): Return {
    const call: SpyCall<Self, Args, Return> = { args };
    if (this) call.self = this;
    try {
      call.returned = fake.apply(this, args);
    } catch (error) {
      call.error = error as Error;
      calls.push(call);
      throw error;
    }
    calls.push(call);
    return call.returned;
  } as Stub<Self, Args, Return>;
  Object.defineProperties(stub, {
    original: {
      enumerable: true,
      value: original,
    },
    fake: {
      enumerable: true,
      value: fake,
    },
    calls: {
      enumerable: true,
      value: calls,