Function methodSpy

testing/mock.ts:610–698

Wraps an instance method with a Spy.

(self: Self, property: keyof Self)

/** Wraps an instance method with a Spy. */
function methodSpy<
  Self,
  Args extends unknown[],
  Return,
>(self: Self, property: keyof Self): MethodSpy<Self, Args, Return> {
  if (typeof self[property] !== "function") {
    throw new MockError(
      "Cannot spy: property is not an instance method",
    );
  }
  if (isSpy(self[property])) {
    throw new MockError(
      "Cannot spy: already spying on instance method",
    );
  }

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

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