Writing test functions in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a test function in Deno.

Deno

Deno.test("example test", () => {
  const result = 1 + 1;
  if (result !== [1]) throw new Error("Test failed");
});

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

A4

B3

C2

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong expected value like 3 or 1.

Forgetting to compare the result properly.

The test checks if 1 + 1 equals 2, so the correct expected value is 2.

2fill in blank

medium

Complete the code to import the assertEquals function from Deno's standard testing library.

Deno

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

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

AassertEquals

BassertThrows

Cassert

DassertNotEquals

Attempts:

3 left

💡 Hint

Common Mistakes

Importing assert instead of assertEquals.

Using assertThrows when not testing errors.

assertEquals is used to compare expected and actual values in tests.

3fill in blank

hard

Fix the error in the test function by completing the assertion call.

Deno

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

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

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

AassertNotEquals

BassertThrows

Cassert

DassertEquals

Attempts:

3 left

💡 Hint

Common Mistakes

Using assertThrows which is for error testing.

Using assertNotEquals which checks for inequality.

assertEquals is used to check if sum equals 5.

4fill in blank

hard

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

Deno

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

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

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.

Not importing assertThrows properly.

assertThrows is used to check if a function throws an error.

5fill in blank

hard

Fill all three blanks to write a test that checks if a function returns the expected value.

Deno

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

function greet(name) {
  return `Hello, ${name}!`;
}

Deno.test("greet test", () => {
  const message = greet("Alice");
  [2](message, [3]);
});

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

AassertEquals

Bassert

C`Hello, Alice!`

D`Hi, Alice!`

Attempts:

3 left

💡 Hint

Common Mistakes

Using assert instead of assertEquals.

Using the wrong expected string.

assertEquals is imported and used to check if the message equals the expected greeting string.

Practice

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

easy

A. To write test functions that check if code works correctly

B. To run the main application server

C. To format code automatically

D. To deploy code to the cloud

Solution

1. Step 1: Understand the role of deno.test

   deno.test is used to define test functions that verify code behavior.

2. Step 2: Differentiate from other tasks

   Running servers, formatting, or deploying are not related to deno.test.

3. Final Answer:

   To write test functions that check if code works correctly -> Option A

4. Quick Check:

   Test functions = deno.test usage [OK]

Hint: Tests check code correctness using deno.test [OK]

Common Mistakes:

• Confusing test functions with running servers
• Thinking deno.test formats code
• Assuming deno.test deploys code

2. Which of the following is the correct syntax to define a test function in Deno?

easy

A. test(() => { /* test code */ });

B. test.deno(() => { /* test code */ });

C. deno.runTest(() => { /* test code */ });

D. deno.test(() => { /* test code */ });

Solution

1. Step 1: Recall correct Deno test syntax

   The correct way to define a test is deno.test(() => { ... }).

2. Step 2: Identify incorrect options

   Options B, C, and D use wrong method names or missing namespace.

3. Final Answer:

   deno.test(() => { /* test code */ }); -> Option D

4. Quick Check:

   Correct test syntax = deno.test [OK]

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

Common Mistakes:

• Swapping method names like test.deno or deno.runTest
• Omitting 'deno.' prefix
• Using just test() without import or context

3. What will be the output when running this test code in Deno?

import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
deno.test("sum test", () => {
  const result = 2 + 3;
  assertEquals(result, 5);
});

medium

A. Runtime error: deno.test is undefined

B. Test fails with assertion error

C. Test passes with no errors

D. Syntax error due to import

Solution

1. Step 1: Analyze the test logic

   The test calculates 2 + 3 and checks if it equals 5, which is true.

2. Step 2: Check for syntax or runtime issues

   The import and usage of deno.test and assertEquals are correct.

3. Final Answer:

   Test passes with no errors -> Option C

4. Quick Check:

   Correct assertion means test passes [OK]

Hint: Correct assertEquals means test passes [OK]

Common Mistakes:

• Assuming test fails when assertion is true
• Thinking import causes syntax error
• Confusing runtime errors with correct usage

4. Identify the error in this Deno test code:

import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
deno.test("check value", () => {
  const value = 10;
  assertEquals(value, "10");
});

medium

A. Type mismatch causes assertion failure

B. Missing async keyword in test function

C. Incorrect import URL for assertEquals

D. deno.test requires a name and function separately

Solution

1. Step 1: Check assertion parameters

   The test compares number 10 with string "10", which are not equal.

2. Step 2: Confirm other syntax correctness

   Import URL and test function syntax are correct; async is not required here.

3. Final Answer:

   Type mismatch causes assertion failure -> Option A

4. Quick Check:

   assertEquals fails if types differ [OK]

Hint: assertEquals fails if types differ exactly [OK]

Common Mistakes:

• Thinking async is always needed
• Assuming string and number are equal
• Believing import URL is wrong

5. You want to write a test in Deno that checks if a function getUserName(id) returns a non-empty string for valid IDs. Which test function is best to write?

hard

A. deno.test("user name test", () => { const name = getUserName(1); assertEquals(typeof name, "number"); });

B. deno.test("user name test", () => { const name = getUserName(1); assert(name.length > 0); });

C. deno.test("user name test", () => { const name = getUserName(1); assertEquals(name, ""); });

D. deno.test("user name test", () => { const name = getUserName(1); assertEquals(name, null); });

Solution

1. Step 1: Understand the test goal

   The test should verify the returned name is a non-empty string.

2. Step 2: Evaluate each option

   deno.test("user name test", () => { const name = getUserName(1); assert(name.length > 0); }); checks if length > 0, which matches the goal. Options A, B, and D check for number type, empty string, or null, which are incorrect.

3. Final Answer:

   deno.test("user name test", () => { const name = getUserName(1); assert(name.length > 0); }); -> Option B

4. Quick Check:

   Check non-empty string with length > 0 [OK]

Hint: Check string length > 0 to confirm non-empty [OK]

Common Mistakes:

• Checking for empty string instead of non-empty
• Checking wrong type like number or null
• Using assertEquals with wrong expected value