Chapter 18: Testing

1. Why Tests Matter More Than You Think

Friday afternoon. Your client reports a critical bug in production. You fix it -- one line. But did that fix break something else? 47 routes. 12 ORM models. 3 middleware functions. Clicking through every page takes an hour. Running the test suite takes 2 seconds.

npm test

Running tests...

  add
    + add([[5, 3]]) == 8
    + add([[null]]) raises Error

  isEven
    + isEven([[4]]) is truthy
    + isEven([[3]]) is falsy

  4 tests: 4 passed, 0 failed, 0 errors

Everything still works. Deploy with confidence. Weekend intact.

Tina4 ships an inline testing framework. No external packages. No Jest configuration. No setup ceremony.

---

2. Your First Test

Tina4's testing framework uses a decorator-style pattern. Attach test assertions directly to functions using tests(), assertEqual(), assertThrows(), assertTrue(), and assertFalse(). Then call runAllTests() to execute them.

Create tests/basic.ts:

import { tests, assertEqual, assertThrows, assertTrue, assertFalse, runAllTests } from "tina4-nodejs";

const add = tests(
    assertEqual([5, 3], 8),
    assertEqual([0, 0], 0),
    assertThrows(Error, [null]),
)(function add(a: number, b: number | null = null): number {
    if (b === null) throw new Error("b required");
    return a + b;
});

const isEven = tests(
    assertTrue([4]),
    assertFalse([3]),
)(function isEven(n: number): boolean {
    return n % 2 === 0;
});

runAllTests();

Run it:

tina4 test

  add
    + add([[5, 3]]) == 8
    + add([[0, 0]]) == 0
    + add([[null]]) raises Error

  isEven
    + isEven([[4]]) is truthy
    + isEven([[3]]) is falsy

  5 tests: 5 passed, 0 failed, 0 errors

How It Works

1. The tests() function takes assertion objects and returns a decorator.
2. The decorator wraps the function, registers it in the test registry, and returns the original function unchanged.
3. The function works normally in production code -- tests only execute when you call runAllTests().
4. Named functions produce readable output. Anonymous functions show as "anonymous."

---

3. Assertion Functions

Function	Description
assertEqual(args, expected)	Call the function with args array, expect expected as the return value
assertThrows(ErrorClass, args)	Call the function with args array, expect it to throw ErrorClass
assertTrue(args)	Call the function with args array, expect a truthy return value
assertFalse(args)	Call the function with args array, expect a falsy return value

Each assertion specifies the arguments to pass and the expected outcome. The args parameter is always an array of arguments.

assertEqual

assertEqual([5, 3], 8)     // Call with 5, 3 -- expect 8
assertEqual(["hello"], 5)  // Call with "hello" -- expect 5

assertThrows

assertThrows(Error, [null])         // Expect Error when called with null
assertThrows(TypeError, ["bad"])    // Expect TypeError when called with "bad"

assertTrue / assertFalse

assertTrue([4])     // Expect a truthy return value
assertFalse([0])    // Expect a falsy return value

---

4. Testing Business Logic

import { tests, assertEqual, assertThrows, runAllTests } from "tina4-nodejs";

const calculateDiscount = tests(
    assertEqual([100, 10], 90),
    assertEqual([50, 0], 50),
    assertEqual([200, 50], 100),
    assertThrows(Error, [100, -5]),
    assertThrows(Error, [100, 101]),
)(function calculateDiscount(price: number, discountPercent: number): number {
    if (discountPercent < 0 || discountPercent > 100) {
        throw new Error("Discount must be between 0 and 100");
    }
    return price - (price * discountPercent / 100);
});

runAllTests();

The function works in production. The tests run only when you call runAllTests().

---

5. Testing ORM Models

Test your models by writing functions that exercise create, read, update, and delete:

import { tests, assertTrue, assertEqual, runAllTests } from "tina4-nodejs";
import { Database } from "tina4-nodejs/orm";

const testCreateProduct = tests(
    assertTrue([]),
)(function testCreateProduct(): boolean {
    const product = new Product({
        name: "Test Widget",
        category: "Testing",
        price: 19.99,
    });
    product.save();
    return product.id !== undefined && product.id > 0;
});

const testLoadProduct = tests(
    assertTrue([]),
)(function testLoadProduct(): boolean {
    const product = new Product({ name: "Load Test", price: 29.99 });
    product.save();

    const loaded = Product.findById(product.id);
    return loaded !== null && loaded.name === "Load Test";
});

const testUpdateProduct = tests(
    assertTrue([]),
)(function testUpdateProduct(): boolean {
    const product = new Product({ name: "Update Test", price: 10 });
    product.save();

    product.name = "Updated Widget";
    product.price = 15;
    product.save();

    const reloaded = Product.findById(product.id);
    return reloaded !== null && reloaded.name === "Updated Widget" && reloaded.price === 15;
});

const testDeleteProduct = tests(
    assertTrue([]),
)(function testDeleteProduct(): boolean {
    const product = new Product({ name: "Delete Me", price: 5 });
    product.save();
    const id = product.id;

    product.delete();

    const gone = Product.findById(id);
    return gone === null;
});

runAllTests();

Test Database

Use a separate database for tests so development data stays safe:

TINA4_TEST_DATABASE_URL=sqlite:///data/test.db

---

6. Testing Routes

Write functions that exercise your API endpoints end-to-end:

import { tests, assertTrue, assertEqual, runAllTests } from "tina4-nodejs";

const testHealthEndpoint = tests(
    assertTrue([]),
)(function testHealthEndpoint(): boolean {
    // Use the test client to send HTTP requests
    const resp = testClient.get("/health");
    return resp.status === 200 && resp.body.status === "ok";
});

const testCreateProduct = tests(
    assertTrue([]),
)(function testCreateProduct(): boolean {
    const resp = testClient.post("/api/products", {
        name: "Route Test Product",
        category: "Testing",
        price: 42,
    });
    return resp.status === 201 && resp.body.name === "Route Test Product";
});

const testGetNotFound = tests(
    assertTrue([]),
)(function testGetNotFound(): boolean {
    const resp = testClient.get("/api/products/99999");
    return resp.status === 404;
});

runAllTests();

---

7. Testing Authentication

import { tests, assertTrue, runAllTests, Auth } from "tina4-nodejs";

const secret = "test-secret";

const testTokenRoundTrip = tests(
    assertTrue([{ userId: 1, role: "admin" }]),
)(function testTokenRoundTrip(payload: Record<string, unknown>): boolean {
    const token = Auth.getToken(payload, secret);
    const decoded = Auth.validToken(token, secret);
    return decoded !== null && decoded.userId === payload.userId;
});

const testPasswordHash = tests(
    assertTrue(["securePass123"]),
    assertTrue(["another-password"]),
)(function testPasswordHash(password: string): boolean {
    const hash = Auth.hashPassword(password);
    return Auth.checkPassword(password, hash);
});

const testInvalidToken = tests(
    assertTrue([]),
)(function testInvalidToken(): boolean {
    const decoded = Auth.validToken("invalid.token.here", secret);
    return decoded === null;
});

runAllTests();

---

8. Resetting Tests Between Files

When running tests across multiple files, use resetTests() to clear the registry:

import { resetTests, tests, assertEqual, runAllTests } from "tina4-nodejs";

resetTests();

const multiply = tests(
    assertEqual([3, 4], 12),
    assertEqual([0, 5], 0),
)(function multiply(a: number, b: number): number {
    return a * b;
});

runAllTests();

Without resetting, tests from previously imported modules accumulate in the registry.

---

9. Runner Options

runAllTests() accepts an options object:

// Quiet mode -- no console output, returns results only
const results = runAllTests({ quiet: true });
console.log(`${results.passed} passed, ${results.failed} failed`);

// Fail fast -- stop on the first failure
runAllTests({ failfast: true });

The returned TestResults object:

Property	Type	Description
passed	number	Assertions that passed
failed	number	Assertions that failed
errors	number	Unexpected errors
details	array	Array of { name, status, message? } objects

CI Integration

Use the return value for CI exit codes:

const results = runAllTests();
process.exit(results.failed === 0 ? 0 : 1);

---

10. Running Tests

Run All Tests

npm test

This runs tests/run-all.ts which discovers and executes all test files.

Run a Specific Test File

tina4 test tests/basic.ts

With npm Scripts

Add to package.json:

{
  "scripts": {
    "test": "npx tsx tests/run-all.ts",
    "test:products": "npx tsx tests/products.ts",
    "test:auth": "npx tsx tests/auth.ts"
  }
}

---

11. Testing Best Practices

Test One Thing Per Function

Each test function should verify one behavior. When it fails, you know exactly what broke.

// Good: each function tests one thing
const testCreateReturnsId = tests(
    assertTrue([]),
)(function testCreateReturnsId(): boolean {
    const product = new Product({ name: "Widget", price: 9.99 });
    product.save();
    return product.id > 0;
});

const testCreateSetsDefaults = tests(
    assertTrue([]),
)(function testCreateSetsDefaults(): boolean {
    const product = new Product({ name: "Widget", price: 9.99 });
    product.save();
    return product.category === "Uncategorized";
});

Use Named Functions for Readable Output

// Good: readable test names
const testLoginRejects = tests(assertTrue([]))(
    function testLoginRejectsInvalidPassword(): boolean { /* ... */ }
);

// Bad: anonymous function
const test = tests(assertTrue([]))(
    () => { /* shows as "anonymous" in output */ }
);

Isolate Tests

Each test should create its own data. Never depend on data from another test or from the development database.

// Good: creates its own data
function testDeleteProduct(): boolean {
    const product = new Product({ name: "Temporary", price: 1 });
    product.save();
    product.delete();
    return Product.findById(product.id) === null;
}

// Bad: depends on external state
function testDeleteProduct(): boolean {
    const product = Product.findById(1); // Assumes ID 1 exists
    product.delete();
    return true;
}

Use Unique Values

Prevent unique constraint failures by generating unique data:

function testCreateUser(): boolean {
    const email = `test-${Date.now()}@example.com`;
    const user = new User({ name: "Test User", email });
    user.save();
    return user.id > 0;
}

---

12. Failed Test Output

When a test fails, the output shows exactly what went wrong:

  calculateDiscount
    + calculateDiscount([[100, 10]]) == 90
    - calculateDiscount([[200, 50]]) == 100
      Expected: 100
      Got: 150
    + calculateDiscount([[100, -5]]) raises Error

  3 tests: 2 passed, 1 failed, 0 errors

The failure message shows the function name, the arguments, what was expected, and what was received. Find the line. Fix the logic. Run again.

---

13. Exercise: Write Tests for Utility Functions

Write inline tests for the following functions:

1. A slugify function that converts "Hello World" to "hello-world"
2. A clamp function that constrains a number between a min and max
3. A parsePrice function that extracts a number from "$19.99" and throws on invalid input

---

14. Solution

import { tests, assertEqual, assertThrows, runAllTests } from "tina4-nodejs";

const slugify = tests(
    assertEqual(["Hello World"], "hello-world"),
    assertEqual(["  Multiple   Spaces  "], "multiple-spaces"),
    assertEqual(["UPPERCASE"], "uppercase"),
    assertEqual(["already-slugged"], "already-slugged"),
)(function slugify(input: string): string {
    return input.trim().toLowerCase().replace(/\s+/g, "-");
});

const clamp = tests(
    assertEqual([5, 0, 10], 5),
    assertEqual([-5, 0, 10], 0),
    assertEqual([15, 0, 10], 10),
    assertEqual([0, 0, 0], 0),
)(function clamp(value: number, min: number, max: number): number {
    return Math.min(Math.max(value, min), max);
});

const parsePrice = tests(
    assertEqual(["$19.99"], 19.99),
    assertEqual(["$0.50"], 0.5),
    assertThrows(Error, ["not-a-price"]),
    assertThrows(Error, [""]),
)(function parsePrice(input: string): number {
    const match = input.match(/\$?([\d.]+)/);
    if (!match) throw new Error("Invalid price format");
    const value = parseFloat(match[1]);
    if (isNaN(value)) throw new Error("Invalid price format");
    return value;
});

runAllTests();

---

15. Gotchas

1. The tests() Decorator Returns the Original Function

The wrapped function works identically in production. Tests only run when you call runAllTests(). You can use the decorated function in your application code without side effects.

2. Arguments Are Passed as an Array

assertEqual([5, 3], 8) means "call the function with arguments 5 and 3, expect 8." The first argument is always an array.

3. Named Functions Are Required for Readable Output

Anonymous functions show up as "anonymous" in test output. Use named function expressions: function testCreateProduct() {} not () => {}.

4. Call resetTests() Between Separate Test Files

Without resetting, tests from previously imported modules accumulate in the registry. Each test file should call resetTests() at the top.

5. runAllTests() Returns Results

Use the return value for CI integration. Check results.failed === 0 to determine the exit code. Without this, your CI pipeline passes even when tests fail.

6. Database State Carries Between Tests

Problem: A test fails because a previous test left data in the database.

Fix: Each test should create its own data and clean up after itself. Use a separate test database. Reset it before each test run.

7. Async Functions Need Special Handling

Problem: You test an async function but the test finishes before the Promise resolves.

Fix: Wrap async operations in a synchronous test function that blocks on the result. Or structure your test to validate the return value of the resolved Promise.