jest-purify-support.ts

import type { Either } from "purify-ts";
import { matcherHint } from "jest-matcher-utils";
import { diff } from "jest-diff";

const passMessage = (expect: "Left" | "Right") => () =>
  matcherHint(`.not.to${expect}`, "received", "") +
  "\n\n" +
  `Expected Either to be ${expect}`;

const failMessage = (expect: "Left" | "Right") => () =>
  matcherHint(`.toBe${expect}`, "received", "") +
  "\n\n" +
  `Expected Either to be ${expect}`;

const failRight = (value: string) => () =>
  matcherHint(".toEqualRight", "received", "") +
  "\n\n" +
  "Expected Either to be Right, received Left." +
  "\n\n" +
  value;

expect.extend({
  toBeRight(received: Either<unknown, unknown>) {
    const pass = received.isRight();
    return {
      pass: pass,
      message: pass ? passMessage("Right") : failMessage("Right"),
    };
  },
  toBeLeft(received: Either<unknown, unknown>) {
    const pass = received.isLeft();
    return {
      pass: pass,
      message: pass ? passMessage("Left") : failMessage("Left"),
    };
  },
  toEqualRight(received: Either<unknown, unknown>, expected: unknown) {
    const { equals, utils, expand } = this;
    const options = {
      comment: "Right value equality",
      isNot: this.isNot,
      promise: this.promise,
    };

    return received.caseOf({
      Left(value) {
        return {
          pass: false,
          message: failRight(utils.printReceived(value)),
        };
      },
      Right(value) {
        if (equals(value, expected)) {
          return {
            pass: true,
            message: passMessage("Right"),
          };
        } else {
          return {
            pass: false,
            message: () => {
              const diffString = diff(expected, received, {
                expand,
              });

              return (
                utils.matcherHint(
                  "toEqualRight",
                  undefined,
                  undefined,
                  options
                ) +
                "\n\n" +
                (diffString && diffString.includes("- Expect")
                  ? `Difference:\n\n${diffString}`
                  : `Expected: ${utils.printExpected(expected)}\n` +
                    `Received: ${utils.printReceived(received)}`)
              );
            },
          };
        }
      },
    });
  },
});