Test steps for organized output in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Deno testing module.

Deno

import { [1] } from "https://deno.land/std/testing/asserts.ts";

Drag options to blanks, or click blank then click option'

AassertEquals

Bassert

CassertThrows

DassertNotEquals

Attempts:

3 left

💡 Hint

Common Mistakes

Importing a wrong assert function that doesn't check equality.

Forgetting to import any function.

The assertEquals function is imported to compare expected and actual values in tests.

2fill in blank

medium

Complete the code to define a test step with a descriptive name.

Deno

Deno.test("[1]", () => {
  // test code here
});

Drag options to blanks, or click blank then click option'

AInitialize database

BRun server

CStart app

DCheck addition works

Attempts:

3 left

💡 Hint

Common Mistakes

Using vague or unrelated test names.

Leaving the test name empty.

The test name should describe what the test checks, like 'Check addition works'.

3fill in blank

hard

Fix the error in the test assertion to compare expected and actual values.

Deno

Deno.test("Sum test", () => {
  const result = 2 + 3;
  [1](result, 5);
});

Drag options to blanks, or click blank then click option'

AassertEquals

Bassert

CassertThrows

DassertNotEquals

Attempts:

3 left

💡 Hint

Common Mistakes

Using assert which only checks truthiness.

Using assertThrows which expects an error.

assertEquals compares two values for equality, which is needed here.

4fill in blank

hard

Fill both blanks to create a test step that checks if a function throws an error.

Deno

Deno.test("Error test", () => {
  [1](() => {
    throw new Error("fail");
  });
  [2](true);
});

Drag options to blanks, or click blank then click option'

AassertThrows

BassertEquals

Cassert

DassertNotEquals

Attempts:

3 left

💡 Hint

Common Mistakes

Using assertEquals instead of assertThrows for error checking.

Leaving the second blank empty or incorrect.

assertThrows checks if the function throws an error, and assert can be used to confirm a condition if needed.

5fill in blank

hard

Fill all three blanks to create a test that checks if a string includes a substring.

Deno

Deno.test("Substring test", () => {
  const text = "hello world";
  const hasHello = text.[1]("hello");
  [2](hasHello);
  [3](hasHello, true);
});

Drag options to blanks, or click blank then click option'

Aincludes

Bassert

CassertEquals

DstartsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using startsWith instead of includes.

Using assertNotEquals or wrong assert functions.

The includes method checks if the string contains a substring. assert asserts the boolean is truthy, and assertEquals compares the value to true.

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