@clipboard-health/testing-core

TypeScript-friendly testing utilities.

Table of contents

• Install
• Usage
  • Type narrowing expect helpers
• Local development commands

Install

npm install @clipboard-health/testing-core

Usage

Type narrowing expect helpers

Jest's expect(...).toBeDefined() does not narrow types.

This gives a type error:

const value = getValue(); // returns 'string | undefined'

expect(value).toBeDefined();

const { length } = value;
// ^? Property 'length' does not exist on type 'string | undefined'.

This library's helpers narrow types:

import { ok } from "node:assert/strict";

import { expectToBeDefined } from "@clipboard-health/testing-core";

function getValue(): string | undefined {
  return "hi";
}

const value = getValue();
expectToBeDefined(value);

// Narrowed to `string`
const { length } = value;
ok(length === 2);

import { ok } from "node:assert/strict";

import { expectToBeLeft } from "@clipboard-health/testing-core";
import { either as E } from "@clipboard-health/util-ts";

function divide(numerator: number, denominator: number): E.Either<string, number> {
  if (denominator === 0) {
    return E.left("Cannot divide by zero");
  }

  return E.right(numerator / denominator);
}

const value = divide(10, 0);
expectToBeLeft(value);

// Narrowed to Left
ok(value.left === "Cannot divide by zero");

import { ok } from "node:assert/strict";

import { expectToBeRight } from "@clipboard-health/testing-core";
import { either as E } from "@clipboard-health/util-ts";

function divide(numerator: number, denominator: number): E.Either<string, number> {
  if (denominator === 0) {
    return E.left("Cannot divide by zero");
  }

  return E.right(numerator / denominator);
}

const value = divide(10, 2);
expectToBeRight(value);

// Narrowed to Right
ok(value.right === 5);

import { ok } from "node:assert/strict";

import { expectToBeDefined, expectToBeSafeParseError } from "@clipboard-health/testing-core";
import { z } from "zod";

const schema = z.object({ name: z.string() });

const value = schema.safeParse({ name: 1 });
expectToBeSafeParseError(value);

// Narrowed to `SafeParseError`
const firstIssue = value.error.issues[0];
expectToBeDefined(firstIssue);

// Narrowed to `ZodIssue`
ok(firstIssue.message === "Expected string, received number");

import { ok } from "node:assert/strict";

import { expectToBeSafeParseSuccess } from "@clipboard-health/testing-core";
import { z } from "zod";

const schema = z.object({ name: z.string() });

const value = schema.safeParse({ name: "hi" });
expectToBeSafeParseSuccess(value);

// Narrowed to `SafeParseSuccess`
ok(value.data.name === "hi");

Local development commands

See package.json scripts for a list of commands.