deno test for testing - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of deno test?

It runs test files in a Deno project to check if the code works as expected.

beginner

How do you define a simple test in Deno?

Use the Deno.test() function with a name and a function containing assertions.

beginner

What does the assertEquals function do in Deno tests?

It checks if two values are equal and throws an error if they are not.

intermediate

How can you run tests with detailed output in Deno?

Use deno test --verbose to see each test's name and result.

intermediate

Can Deno tests be asynchronous? How?

Yes, by making the test function async and using await inside it.

Which command runs tests in a Deno project?

A deno test

B deno run

C deno build

D deno start

deno test runs all test files and functions in the project.

What is the correct way to import assertion functions in Deno tests?

A import assertEquals from 'assert';

B import { assertEquals } from 'deno/testing';

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

D No import needed, assertions are global.

Deno provides assertion functions from its standard library URL.

How do you mark a test as asynchronous in Deno?

A Add async: true in test options.

B Make the test function async and use await inside.

C Use Deno.asyncTest() instead of Deno.test().

D Deno tests cannot be asynchronous.

Simply declare the test function async to use await inside.

What happens if an assertion fails in a Deno test?

A The test is skipped.

B The test passes anyway.

C Deno crashes.

D The test fails and shows an error message.

A failed assertion causes the test to fail and prints details.

Which flag shows detailed test results in Deno?

A --verbose

B --quiet

C --silent

D --fast

The --verbose flag shows each test name and result.

Explain how to write and run a basic test in Deno.

Think about how you tell Deno what to test and how to check results.

Describe how asynchronous code can be tested using Deno test.

Remember async/await in JavaScript and how tests can wait for promises.

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