README.md

@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 { strictEqual } 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;
strictEqual(length, 2);

import { strictEqual } 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
strictEqual(value.left, "Cannot divide by zero");

import { strictEqual } 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
strictEqual(value.right, 5);

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

import { expectToBeFailure } from "@clipboard-health/testing-core";
import { failure, type ServiceResult, success } from "@clipboard-health/util-ts";

function validateAge(age: number): ServiceResult<number> {
  if (age < 0) {
    return failure({ issues: [{ code: "INVALID_AGE", message: "Age cannot be negative" }] });
  }

  return success(age);
}

const result = validateAge(-5);
expectToBeFailure(result);

// Narrowed to Left (Failure)
strictEqual(result.left.issues[0]?.message, "Age cannot be negative");

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

import { expectToBeSuccess } from "@clipboard-health/testing-core";
import { failure, type ServiceResult, success } from "@clipboard-health/util-ts";

function validateAge(age: number): ServiceResult<number> {
  if (age < 0) {
    return failure({ issues: [{ code: "INVALID_AGE", message: "Age cannot be negative" }] });
  }

  return success(age);
}

const result = validateAge(25);
expectToBeSuccess(result);

// Narrowed to Right (Success)
strictEqual(result.right, 25);

import { strictEqual } 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;
expectToBeDefined(firstIssue);

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

import { strictEqual } 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`
strictEqual(value.data.name, "hi");

Local development commands

See package.json scripts for a list of commands.