deno test for testing - Mini Project: Build & Apply

Basic Testing with Deno Test

📖 Scenario: You are building a small utility function in Deno and want to make sure it works correctly by writing tests.

🎯 Goal: Create a simple function and write a test for it using deno test to verify it behaves as expected.

📋 What You'll Learn

Create a function named add that takes two numbers and returns their sum.

Create a variable expected with the value of the expected sum.

Write a test using Deno.test that checks if add returns the correct sum.

Use assertEquals from std/testing/asserts.ts to compare actual and expected values.

💡 Why This Matters

🌍 Real World

Testing code helps catch errors before your program runs for real users. It is like double-checking your work to avoid mistakes.

💼 Career

Many jobs require writing tests to ensure software works correctly and reliably. Knowing how to use <code>deno test</code> is useful for Deno and JavaScript developers.

1

Create the add function

Write a function named add that takes two parameters a and b and returns their sum using return a + b.

Deno

// Write the add function here
// Your code here

Hint

Think of add as a calculator that adds two numbers and gives back the result.

2

Create the expected result variable

Create a variable named expected and set it to the number 7.

Deno

function add(a, b) {
  return a + b;
}

// Create expected variable here
// Your code here

Hint

This is the number you expect when adding 3 and 4.

3

Write a test using Deno.test

Write a test using Deno.test with the name "add function test". Inside the test, call add(3, 4) and store the result in a variable named result.

Deno

function add(a, b) {
  return a + b;
}

const expected = 7;

// Write Deno.test here
// Your code here

Hint

Use Deno.test to create a test block and call the add function inside it.

4

Use assertEquals to check the result

Import assertEquals from "https://deno.land/std/testing/asserts.ts". Inside the test, use assertEquals(result, expected) to verify the function output matches the expected value.

Deno

import { assertEquals } from "https://deno.land/std/testing/asserts.ts";

function add(a, b) {
  return a + b;
}

const expected = 7;

Deno.test("add function test", () => {
  const result = add(3, 4);
  // Use assertEquals here
  // Your code here
});

Hint

This checks if the actual result matches what you expect. If they don't match, the test will fail.

Practice

1. What is the main purpose of using deno test in your code?

easy

A. To check if your code works as expected by running tests

B. To deploy your code to a server

C. To format your code automatically

D. To create a new Deno project

Solution

1. Step 1: Understand the role of deno test

   deno test is a command used to run tests written in your code to verify correctness.

2. Step 2: Compare with other options

   Deploying, formatting, or creating projects are not related to testing functionality.

3. Final Answer:

   To check if your code works as expected by running tests -> Option A

4. Quick Check:

   Testing = Check code correctness [OK]

Hint: Remember: testing means checking code correctness [OK]

Common Mistakes:

• Confusing testing with deployment
• Thinking deno test formats code
• Assuming it creates projects

2. Which of the following is the correct way to write a simple test in Deno?

easy

A. deno.test(() => { assertEquals(1 + 1, 2); });

B. test deno { assertEquals(1 + 1, 2); }

C. deno.test = () => { assertEquals(1 + 1, 2); }

D. test(() => assertEquals(1 + 1, 2));

Solution

1. Step 1: Identify correct test syntax in Deno

   The correct syntax uses deno.test as a function with a callback containing assertions.

2. Step 2: Check each option

   deno.test(() => { assertEquals(1 + 1, 2); }); correctly uses deno.test(() => { ... }). Options A, B, and D have syntax errors or incorrect usage.

3. Final Answer:

   deno.test(() => { assertEquals(1 + 1, 2); }); -> Option A

4. Quick Check:

   Correct test syntax = deno.test(() => { assertEquals(1 + 1, 2); }); [OK]

Hint: Use deno.test with a function callback [OK]

Common Mistakes:

• Using incorrect keywords like 'test deno'
• Assigning instead of calling deno.test
• Omitting 'deno.' prefix

3. What will be the output when running this test code with deno test?

import { assertEquals } from "https://deno.land/std@0.177.0/testing/asserts.ts";
deno.test("sum test", () => {
  assertEquals(2 + 2, 4);
});

medium

A. Syntax error due to import statement

B. Test fails with assertion error

C. Test passes with no errors

D. Runtime error: deno.test is not a function

Solution

1. Step 1: Analyze the test code logic

   The test checks if 2 + 2 equals 4 using assertEquals, which is true.

2. Step 2: Consider syntax and runtime

   The import statement is correct, and deno.test is valid in Deno environment.

3. Final Answer:

   Test passes with no errors -> Option C

4. Quick Check:

   Correct assertion = Test passes [OK]

Hint: True assertions mean passing tests [OK]

Common Mistakes:

• Thinking import causes syntax error
• Confusing assertion failure with success
• Assuming deno.test is undefined

4. Identify the error in this test code snippet:

import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
deno.test("check", () => {
  assertEquals(5, 2 + 2);
});

medium

A. assertEquals is not imported correctly

B. The assertion will fail because 5 is not equal to 4

C. deno.test is used incorrectly without a name

D. The import URL is missing the version number

Solution

1. Step 1: Check the import statement

   The import URL lacks a version number, which is required for stable imports in Deno.

2. Step 2: Verify other parts

   The assertion will fail logically, but the question asks for the error in the snippet, and missing version is a syntax/runtime error.

3. Final Answer:

   The import URL is missing the version number -> Option D

4. Quick Check:

   Stable imports need version numbers [OK]

Hint: Always include version in import URLs [OK]

Common Mistakes:

• Ignoring missing version in import URL
• Confusing assertion failure with syntax error
• Assuming deno.test needs no name

5. You want to write multiple tests in one file using deno test. Which approach correctly groups tests with descriptive names and runs them all?

hard

A. Write one deno.test with multiple assertions but no names

B. Use multiple deno.test calls each with a unique name and callback function

C. Call deno.test inside a loop without names

D. Use deno.runTests() to run tests automatically

Solution

1. Step 1: Understand how to organize multiple tests

   Each test should have a unique name and a callback function using deno.test.

2. Step 2: Evaluate options

   Use multiple deno.test calls each with a unique name and callback function correctly uses multiple named tests. Write one deno.test with multiple assertions but no names lacks test names, making results unclear. Call deno.test inside a loop without names uses a loop without names, which is not recommended. Use deno.runTests() to run tests automatically is invalid; deno.runTests() does not exist.

3. Final Answer:

   Use multiple deno.test calls each with a unique name and callback function -> Option B

4. Quick Check:

   Multiple named tests = Use multiple deno.test calls each with a unique name and callback function [OK]

Hint: Name each test separately with deno.test [OK]

Common Mistakes:

• Writing unnamed tests
• Using loops without test names
• Assuming deno.runTests() exists