deno test for testing - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Deno test?

Consider this Deno test code. What will be the test result output when running deno test?

Deno

import { assertEquals } from "https://deno.land/std@0.177.0/testing/asserts.ts";

Deno.test("sum test", () => {
  const result = 2 + 3;
  assertEquals(result, 5);
});

A The test fails with an assertion error.

B The test passes with no errors.

C SyntaxError due to missing async keyword.

D Runtime error because assertEquals is not imported.

💡 Hint

Check if the assertion matches the expected value.

The test checks if 2 + 3 equals 5, which is true, so the test passes without errors.

📝 Syntax

intermediate

Which option causes a syntax error in Deno test?

Identify which test code snippet will cause a syntax error when running deno test.

A Deno.test "test", () => { assertEquals(1, 1); });

B Deno.test("test", async () => { await Promise.resolve(); });

C ;)} ;)1 ,1(slauqEtressa { >= )( ,"tset"(tset.oneD

D Deno.test("test", () => { assertEquals(1, 1); });

💡 Hint

Look for missing parentheses or misplaced quotes.

Option A is missing parentheses after Deno.test causing a syntax error.

❓ state_output

advanced

What is the output of this asynchronous Deno test?

Given this Deno test code, what will be the test output?

Deno

import { assertEquals } from "https://deno.land/std@0.177.0/testing/asserts.ts";

Deno.test("async test", async () => {
  const value = await Promise.resolve(10);
  assertEquals(value, 10);
});

A Test fails due to assertion error.

B Test fails due to unhandled promise rejection.

C Test passes successfully.

D Syntax error because async is not allowed.

💡 Hint

Check if the awaited promise resolves to the expected value.

The promise resolves to 10, matching the assertion, so the test passes.

🔧 Debug

advanced

Which option causes a runtime error in this Deno test?

Find the code snippet that will cause a runtime error when running deno test.

A Deno.test("test", () => { const x = undefinedVariable; });

B Deno.test("test", () => { 1 === 1; });

C Deno.test("test", () => { return true; });

D Deno.test("test", () => { throw new Error("fail"); });

💡 Hint

Look for undefined variables causing errors.

Option A references an undefined variable causing a ReferenceError at runtime.

🧠 Conceptual

expert

How many tests will run and what is the output?

Given this Deno test file, how many tests will run and what will be the overall result?

Deno

import { assertEquals } from "https://deno.land/std@0.177.0/testing/asserts.ts";

Deno.test("test 1", () => {
  assertEquals(1 + 1, 2);
});

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

Deno.test("test 3", () => {
  assertEquals(3 * 3, 9);
});

A 3 tests run; all pass successfully.

B 2 tests run; 1 pass, 1 fails.

C 1 test runs and it fails.

D 3 tests run; 2 pass, 1 fails with error.

💡 Hint

Count all deno.test calls and check which throw errors.

All three tests run. Test 2 throws an error causing failure; tests 1 and 3 pass.

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