Code coverage reporting in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run tests with coverage reporting in Deno.

Deno

deno test --[1]=coverage

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

Awatch

Ballow-read

Cunstable

Dcoverage

Attempts:

3 left

💡 Hint

Common Mistakes

Using flags unrelated to coverage like --allow-read

Forgetting the double dashes before the flag

The --coverage flag tells Deno to collect coverage data when running tests.

2fill in blank

medium

Complete the command to generate a coverage report in lcov format.

Deno

deno coverage --[1]=lcov

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

Afile

Bformat

Creport

Doutput

Attempts:

3 left

💡 Hint

Common Mistakes

Using --output instead of --format

Using --file which is not a valid option here

The --format option specifies the output format of the coverage report.

3fill in blank

hard

Fix the error in the command to save coverage data to a file named 'cov.json'.

Deno

deno coverage --[1] cov.json

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

Asave

Bfile

Coutput

Dreport

Attempts:

3 left

💡 Hint

Common Mistakes

Using --save which is not a recognized flag

Using --file which is invalid in this context

The correct flag to specify the output file is --output.

4fill in blank

hard

Fill both blanks to run tests with coverage and specify the output directory as 'coverage_data'.

Deno

deno test --[1] --[2]=coverage_data

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

Acoverage

Boutput

Callow-read

Dunstable

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up flags or using invalid ones like --allow-read

Forgetting to use the equals sign for the output directory

Use --coverage to enable coverage collection and --output to specify the directory.

5fill in blank

hard

Fill all three blanks to generate a coverage report in text format, saving it to 'report.txt'.

Deno

deno coverage --[1]=text --[2]=report.txt --[3]

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

Aformat

Boutput

Cunstable

Dallow-read

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the --unstable flag causing errors

Using wrong flags for format or output

Use --format=text for text output, --output=report.txt to save, and --unstable because coverage commands may require it.

Practice

1. What does the deno test --coverage command do?

easy

A. Installs coverage tools for Deno

B. Only runs tests without coverage data

C. Generates a coverage report without running tests

D. Runs tests and collects code coverage data

Solution

1. Step 1: Understand the purpose of deno test --coverage

   This command runs your test files and collects data on which parts of your code were executed during testing.

2. Step 2: Differentiate from other commands

   Unlike just running tests, this command also tracks coverage. It does not generate reports directly; that is done by deno coverage.

3. Final Answer:

   Runs tests and collects code coverage data -> Option D

4. Quick Check:

   deno test --coverage collects coverage data [OK]

Hint: Remember: test runs + coverage data collection together [OK]

Common Mistakes:

• Thinking it only runs tests without coverage
• Confusing coverage data collection with report generation
• Assuming it installs tools instead of running tests

2. Which of the following is the correct command to view a coverage report in the terminal?

easy

A. deno coverage --reporter=text

B. deno test --view-coverage

C. deno coverage --show

D. deno test --coverage-report

Solution

1. Step 1: Identify the command to view coverage

   The deno coverage command is used to view or export coverage reports after running tests with coverage.

2. Step 2: Recognize the correct flag for terminal output

   The flag --reporter=text tells Deno to show the coverage report in the terminal.

3. Final Answer:

   deno coverage --reporter=text -> Option A

4. Quick Check:

   Use deno coverage with --reporter=text to view coverage [OK]

Hint: Use deno coverage with --reporter=text to see output [OK]

Common Mistakes:

• Using deno test flags to view coverage report
• Assuming --show or --view-coverage are valid flags
• Confusing test and coverage commands

3. Given the following commands run in order:

deno test --coverage=./cov_data
deno coverage ./cov_data --reporter=lcov

What is the expected output?

medium

A. Tests run but no coverage data is saved

B. A coverage report file in lcov format is generated

C. An error occurs because coverage directory is missing

D. Coverage report is printed directly in the terminal

Solution

1. Step 1: Run tests with coverage saved to a directory

   The first command runs tests and saves coverage data into the folder ./cov_data.

2. Step 2: Generate coverage report in lcov format

   The second command reads coverage data from ./cov_data and outputs a report in lcov format to a file (stdout is the report content, but typically redirected to a file).

3. Final Answer:

   A coverage report file in lcov format is generated -> Option B

4. Quick Check:

   Coverage data saved + lcov report generated [OK]

Hint: Save coverage data first, then generate report from it [OK]

Common Mistakes:

• Expecting coverage report without saving data first
• Thinking lcov generates a file automatically (use redirection)
• Assuming error if directory exists

4. You ran deno test --coverage but deno coverage shows no data. What is the likely cause?

medium

A. Your test files have syntax errors

B. You forgot to specify a coverage directory when running tests

C. You ran deno coverage before running tests

D. Coverage data is automatically deleted after tests

Solution

1. Step 1: Understand coverage data flow

   Coverage data is collected when tests run with coverage enabled and saved to a directory or default location.

2. Step 2: Check command order

   If deno coverage is run before tests, no coverage data exists yet, so it shows no data.

3. Final Answer:

   You ran deno coverage before running tests -> Option C

4. Quick Check:

   Run tests first, then coverage report [OK]

Hint: Always run tests with coverage before viewing reports [OK]

Common Mistakes:

• Assuming coverage directory is mandatory every time
• Thinking syntax errors cause no coverage data
• Believing coverage data auto-deletes after tests

5. You want to generate a coverage report in HTML format and open it in your browser. Which sequence of commands achieves this correctly?

hard

A. deno test --coverage=./cov_data && deno coverage ./cov_data --reporter=html && open coverage/index.html

B. deno coverage --reporter=html && deno test --coverage && open ./cov_data/index.html

C. deno test && deno coverage --reporter=html && open ./cov_data/index.html

D. deno test --coverage && deno coverage --reporter=html > report.html && open report.html

Solution

1. Step 1: Run tests with coverage saved to a directory

   Use deno test --coverage=./cov_data to run tests and save coverage data in ./cov_data.

2. Step 2: Generate HTML report from saved coverage data

   Run deno coverage ./cov_data --reporter=html to create HTML files inside coverage/ directory.

3. Step 3: Open the generated HTML report in browser

   Use open coverage/index.html (macOS) or equivalent to view the report.

4. Final Answer:

   deno test --coverage=./cov_data && deno coverage ./cov_data --reporter=html && open coverage/index.html -> Option A

5. Quick Check:

   Save coverage, generate HTML, then open file [OK]

Hint: Save coverage, generate HTML report, then open it [OK]

Common Mistakes:

• Generating report before running tests
• Not specifying coverage directory consistently
• Redirecting HTML output to file instead of directory