import { isPromise } from "./promise";

describe("utils/promise", () => {
  describe("isPromise", () => {
    it("should return true for a Promise", () => {
      const promise = new Promise<void>((resolve) => {
        resolve();
      });

      expect(isPromise(promise)).toBe(true);
    });

    it("should return true for a Promise created with Promise.resolve", () => {
      const promise = Promise.resolve("test");

      expect(isPromise(promise)).toBe(true);
    });

    it("should return true for a Promise created with Promise.reject (when caught)", () => {
      const promise = Promise.reject("error").catch(() => {});

      expect(isPromise(promise)).toBe(true);
    });

    it("should return false for null", () => {
      expect(isPromise(null)).toBe(false);
    });

    it("should return false for undefined", () => {
      expect(isPromise(undefined)).toBe(false);
    });

    it("should return false for a string", () => {
      expect(isPromise("string")).toBe(false);
    });

    it("should return false for a number", () => {
      expect(isPromise(123)).toBe(false);
    });

    it("should return false for a boolean", () => {
      expect(isPromise(true)).toBe(false);
    });

    it("should return false for a regular object", () => {
      const obj = { key: "value" };

      expect(isPromise(obj)).toBe(false);
    });

    it("should return false for an object with only a then method", () => {
      const thennable = {
        then: () => {},
      };

      expect(isPromise(thennable)).toBe(false);
    });

    it("should return false for an object with non-function then and catch properties", () => {
      const obj = {
        then: "not a function",
        catch: "not a function",
      };

      expect(isPromise(obj)).toBe(false);
    });

    it("should return false for an object with then and catch methods that aren't functions", () => {
      const obj = {
        then: 123,
        catch: true,
      };

      expect(isPromise(obj)).toBe(false);
    });
  });
});