Debugging with WP_DEBUG in Wordpress - Practice Problems & Coding Challenges

Challenge - 5 Problems

🔧 Debug

intermediate

What happens when WP_DEBUG is set to true?

In a WordPress site, if you set define('WP_DEBUG', true); in wp-config.php, what is the expected behavior?

A Nothing changes; WP_DEBUG has no effect.

B The site will automatically fix all PHP errors.

C The site will disable all plugins to prevent errors.

D PHP errors and warnings will be displayed on the site pages.

💡 Hint

Think about what debugging means and what showing errors helps with.

Setting WP_DEBUG to true tells WordPress to show PHP errors and warnings on the site. This helps developers find and fix problems.

❓ component_behavior

intermediate

Effect of WP_DEBUG_DISPLAY set to false

If WP_DEBUG is true but define('WP_DEBUG_DISPLAY', false); is also set, what will happen?

A Errors will be logged but not shown on the site pages.

B Errors will be shown on the site pages and logged.

C Errors will cause the site to crash immediately.

D Errors will be neither logged nor shown.

💡 Hint

Think about separating error display from error logging.

When WP_DEBUG_DISPLAY is false, errors are hidden from the site pages. They are neither logged nor shown unless WP_DEBUG_LOG is enabled.

📝 Syntax

advanced

Correct way to enable error logging in WordPress

Which code snippet correctly enables error logging to a file in WordPress?

A

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);

B

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', 'false');

C

define('WP_DEBUG', false);
define('WP_DEBUG_LOG', true);

D define('WP_DEBUG_LOG', true);

💡 Hint

Both WP_DEBUG and WP_DEBUG_LOG must be true to log errors.

To log errors, WP_DEBUG must be true and WP_DEBUG_LOG must also be true. This combination enables logging to wp-content/debug.log.

❓ state_output

advanced

What file stores logged errors when WP_DEBUG_LOG is true?

When WP_DEBUG_LOG is set to true, where does WordPress save the error logs by default?

A wp-content/uploads/error.log

B wp-content/debug.log

C wp-includes/error.log

D root directory error.log

💡 Hint

Think about the folder where WordPress stores content files.

By default, WordPress saves error logs to wp-content/debug.log when WP_DEBUG_LOG is true.

🧠 Conceptual

expert

Why avoid enabling WP_DEBUG on a live site?

Why is it generally not recommended to have WP_DEBUG set to true on a live WordPress site?

A Because it automatically deletes all user data.

B Because it disables all caching, slowing down the site.

C Because it can expose sensitive error details to visitors, risking security.

D Because it prevents plugins from updating.

💡 Hint

Think about what showing errors publicly might reveal.

Enabling WP_DEBUG on a live site can show error messages to visitors, which might reveal sensitive information and create security risks.

Practice

1. What is the main purpose of enabling WP_DEBUG in WordPress?

easy

A. To speed up the website loading time

B. To display and log PHP errors and warnings for debugging

C. To disable all plugins temporarily

D. To change the website theme automatically

Solution

1. Step 1: Understand WP_DEBUG role

   WP_DEBUG is a constant in WordPress that helps developers see PHP errors and warnings.

2. Step 2: Identify its main use

   It is used to display and log errors to help fix issues during development.

3. Final Answer:

   To display and log PHP errors and warnings for debugging -> Option B

4. Quick Check:

   WP_DEBUG shows errors = B [OK]

Hint: WP_DEBUG shows errors to help fix bugs [OK]

Common Mistakes:

• Thinking WP_DEBUG speeds up the site
• Confusing WP_DEBUG with plugin management
• Assuming WP_DEBUG changes themes

2. Which line correctly enables debugging in the wp-config.php file?

easy

A. define('WP_DEBUG', false);

B. define(WP_DEBUG, true);

C. WP_DEBUG = true;

D. define('WP_DEBUG', true);

Solution

1. Step 1: Check correct syntax for defining constants in PHP

   Constants are defined using define('NAME', value); with quotes around the name.

2. Step 2: Identify correct value to enable debugging

   Setting WP_DEBUG to true enables debugging.

3. Final Answer:

   define('WP_DEBUG', true); -> Option D

4. Quick Check:

   Correct PHP constant syntax with true = C [OK]

Hint: Use define('WP_DEBUG', true); with quotes and semicolon [OK]

Common Mistakes:

• Missing quotes around WP_DEBUG
• Using assignment (=) instead of define()
• Setting WP_DEBUG to false to enable debugging

3. Given this code in wp-config.php:

define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

What happens when a PHP error occurs?

medium

A. Error is logged to debug.log but not shown on the website

B. Error is neither shown nor logged

C. Error is shown on the website and logged to debug.log

D. Error is shown on the website but not logged

Solution

1. Step 1: Analyze WP_DEBUG_DISPLAY setting

   WP_DEBUG_DISPLAY is set to false, so errors are not shown on the website.

2. Step 2: Analyze WP_DEBUG_LOG setting

   WP_DEBUG_LOG is true, so errors are logged to the debug.log file.

3. Final Answer:

   Error is logged to debug.log but not shown on the website -> Option A

4. Quick Check:

   Display false + Log true = A [OK]

Hint: Display false hides errors; log true saves them [OK]

Common Mistakes:

• Assuming errors show on site when WP_DEBUG_DISPLAY is false
• Thinking errors are not logged if not displayed
• Confusing WP_DEBUG_LOG with WP_DEBUG_DISPLAY

4. You enabled WP_DEBUG but no errors appear on your site or in the log file. What is the most likely cause?

medium

A. You forgot to set WP_DEBUG_LOG to true

B. You set WP_DEBUG_DISPLAY to true

C. You set WP_DEBUG to false

D. You did not save the wp-config.php file

Solution

1. Step 1: Check WP_DEBUG status

   WP_DEBUG is enabled, so errors should appear or be logged.

2. Step 2: Check if errors are logged

   If WP_DEBUG_LOG is not true, errors won't be saved to the log file.

3. Final Answer:

   You forgot to set WP_DEBUG_LOG to true -> Option A

4. Quick Check:

   Logging off means no error logs = A [OK]

Hint: Enable WP_DEBUG_LOG to save errors to file [OK]

Common Mistakes:

• Thinking WP_DEBUG_DISPLAY controls logging
• Assuming WP_DEBUG false but errors show
• Not saving wp-config.php after changes

5. You want to debug a plugin error but avoid showing errors to visitors. Which settings in wp-config.php should you use?

hard

A. define('WP_DEBUG', false);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

B. define('WP_DEBUG', false);
define('WP_DEBUG_LOG', false);
define('WP_DEBUG_DISPLAY', true);

C. define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

D. define('WP_DEBUG', true);
define('WP_DEBUG_LOG', false);
define('WP_DEBUG_DISPLAY', true);

Solution

1. Step 1: Enable debugging without showing errors

   Set WP_DEBUG to true to enable debugging and WP_DEBUG_DISPLAY to false to hide errors from visitors.

2. Step 2: Enable logging to capture errors

   Set WP_DEBUG_LOG to true to save errors to the debug.log file for review.

3. Final Answer:

   define('WP_DEBUG', true); define('WP_DEBUG_LOG', true); define('WP_DEBUG_DISPLAY', false); -> Option C

4. Quick Check:

   Debug on + Log on + Display off = D [OK]

Hint: Show no errors but log them with WP_DEBUG_DISPLAY false [OK]

Common Mistakes:

• Turning off WP_DEBUG disables all error reporting
• Showing errors to visitors by setting WP_DEBUG_DISPLAY true
• Not enabling WP_DEBUG_LOG so errors are lost