Test steps for organized output in Deno - Mini Project: Build & Apply

Test steps for organized output

📖 Scenario: You are creating a simple test suite in Deno to check if your functions produce organized output. This helps you ensure your code works as expected step by step.

🎯 Goal: Build a Deno test file with multiple test steps that check output organization using Deno.test and assertEquals.

📋 What You'll Learn

Create a variable called output with the exact string value 'Step 1 complete'.

Create a variable called expected with the exact string value 'Step 1 complete'.

Write a test named 'Check output matches expected' that uses assertEquals(output, expected).

Add a second test named 'Check output length' that asserts output.length === expected.length.

💡 Why This Matters

🌍 Real World

Writing tests helps developers catch errors early and ensures their code behaves as expected before release.

💼 Career

Testing skills are essential for software developers, QA engineers, and anyone involved in software maintenance and quality assurance.

1

DATA SETUP: Create the output string

Create a variable called output and set it to the string 'Step 1 complete'.

Deno

// Your code here

Hint

Use const output = 'Step 1 complete'; to create the variable.

2

CONFIGURATION: Create the expected string

Create a variable called expected and set it to the string 'Step 1 complete'.

Deno

const output = 'Step 1 complete';
// Your code here

Hint

Use const expected = 'Step 1 complete'; to create the expected value.

3

CORE LOGIC: Write a test to compare output and expected

Write a test named 'Check output matches expected' using Deno.test that asserts assertEquals(output, expected). Import assertEquals from "https://deno.land/std@0.203.0/testing/asserts.ts".

Deno

import { assertEquals } from "https://deno.land/std@0.203.0/testing/asserts.ts";

const output = 'Step 1 complete';
const expected = 'Step 1 complete';

// Your code here

Hint

Use Deno.test('Check output matches expected', () => { assertEquals(output, expected); });.

4

COMPLETION: Add a second test to check output length

Add a second test named 'Check output length' using Deno.test that asserts output.length === expected.length with assertEquals.

Deno

import { assertEquals } from "https://deno.land/std@0.203.0/testing/asserts.ts";

const output = 'Step 1 complete';
const expected = 'Step 1 complete';

Deno.test('Check output matches expected', () => {
  assertEquals(output, expected);
});

// Your code here

Hint

Use Deno.test('Check output length', () => { assertEquals(output.length, expected.length); });.

Practice

1. What is the main benefit of organizing test steps clearly in deno.test?

easy

A. Automatically fixes code errors

B. Runs tests faster

C. Reduces the number of tests needed

D. Makes tests easier to read and debug

Solution

1. Step 1: Understand the purpose of test organization

   Organizing test steps clearly helps anyone reading the test understand what each part does.

2. Step 2: Connect organization to debugging ease

   Clear steps make it easier to find where a test fails and fix it quickly.

3. Final Answer:

   Makes tests easier to read and debug -> Option D

4. Quick Check:

   Clear test steps = easier debugging [OK]

Hint: Clear test steps help find bugs faster [OK]

Common Mistakes:

• Thinking organization speeds up test execution
• Believing fewer tests are needed with organization
• Assuming tests fix code automatically

2. Which of the following is the correct way to define a test with a clear name in Deno?

easy

A. deno.check('Check addition', () => { /* test code */ })

B. test('Check addition', () => { /* test code */ })

C. deno.test('Check addition', () => { /* test code */ })

D. deno.runTest('Check addition', () => { /* test code */ })

Solution

1. Step 1: Recall Deno test syntax

   Deno uses the deno.test function to define tests with a name and a function.

2. Step 2: Identify the correct function call

   Only deno.test matches the correct syntax; others are invalid or do not exist.

3. Final Answer:

   deno.test('Check addition', () => { /* test code */ }) -> Option C

4. Quick Check:

   Use deno.test() to define tests [OK]

Hint: Use deno.test() with a descriptive name [OK]

Common Mistakes:

• Using just test() without deno prefix
• Using non-existent functions like deno.check()
• Confusing runTest with test

3. Consider this Deno test code:

deno.test('Sum test', () => {
  const a = 2;
  const b = 3;
  const result = a + b;
  if (result !== 5) throw new Error('Sum failed');
});

What happens when you run this test?

medium

A. Test outputs the sum value

B. Test passes silently with no errors

C. Syntax error stops the test

D. Test fails with 'Sum failed' error

Solution

1. Step 1: Analyze the sum calculation

   Variables a=2 and b=3 sum to 5, so result is 5.

2. Step 2: Check the condition for error

   The condition result !== 5 is false, so no error is thrown.

3. Final Answer:

   Test passes silently with no errors -> Option B

4. Quick Check:

   Correct sum means no error thrown [OK]

Hint: Check if error condition matches actual result [OK]

Common Mistakes:

• Assuming test outputs values automatically
• Thinking test fails without error throw
• Confusing syntax error with runtime error

4. This Deno test code has an error:

deno.test('Check value', () => {
  const val = 10
  if val !== 10 {
    throw new Error('Value mismatch')
  }
});

What is the error and how to fix it?

medium

A. Missing parentheses in if condition; add parentheses

B. Missing semicolon after val declaration; add semicolon

C. Wrong function name; use deno.check instead of deno.test

D. Cannot throw error inside test; remove throw statement

Solution

1. Step 1: Identify syntax error in if statement

   The if condition lacks parentheses around val !== 10, which is required in JavaScript/TypeScript.

2. Step 2: Fix the if statement syntax

   Add parentheses: if (val !== 10) { ... } to correct the syntax.

3. Final Answer:

   Missing parentheses in if condition; add parentheses -> Option A

4. Quick Check:

   If conditions need parentheses [OK]

Hint: Always wrap if conditions in parentheses [OK]

Common Mistakes:

• Ignoring missing parentheses error
• Thinking semicolons cause this error
• Confusing function names in Deno tests

5. You want to organize a Deno test that checks multiple steps: fetching data, validating it, and saving results. Which approach best organizes these steps for clear output?

hard

A. Use one test with clear comments and separate code blocks for each step

B. Write all steps in one line without comments

C. Create multiple tests but with vague names like 'Test 1', 'Test 2'

D. Skip comments and rely on console.log for clarity

Solution

1. Step 1: Understand importance of clear test structure

   Organizing steps with comments and separate code blocks helps readers follow the test flow easily.

2. Step 2: Compare options for clarity

   One test with clear comments is better than vague test names or no comments, which confuse readers.

3. Final Answer:

   Use one test with clear comments and separate code blocks for each step -> Option A

4. Quick Check:

   Clear comments + code blocks = organized tests [OK]

Hint: Comment each step clearly inside one test [OK]

Common Mistakes:

• Writing unclear test names
• Skipping comments thinking code is self-explanatory
• Relying only on console logs for understanding