Add unified diff output to failed Behat comparisons

[Copilot]

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Summary

Successfully improved Behat output to include diffs on failed comparisons, making it much easier to debug test failures.

Completed Tasks

• [x] Add sebastian/diff v3 as a dependency (compatible with PHP 7.2+)
• [x] Create a helper method to generate diffs with proper type hints
• [x] Update check_string method to show diffs when comparisons fail
• [x] Update compare_tables method to show diffs
• [x] Update JSON comparison methods to show diffs with proper error checking
• [x] Update CSV comparison method to show diffs
• [x] Update YAML comparison method to show diffs
• [x] Add parameter and return type hints
• [x] Add error checking for JSON encoding/decoding
• [x] Fix pre-existing bug in CSV comparison variable usage
• [x] Fix typo in YAML docstring
• [x] Verify PHP syntax is correct
• [x] Run code review and address all feedback
• [x] Run security checks
• [x] Update to use sebastian/diff v3 API for PHP 7.2+ compatibility

Changes Summary

3 files changed, 78 insertions(+), 13 deletions(-)

1. composer.json: Added sebastian/diff v3 as an explicit dependency
2. src/Context/Support.php: Added generate_diff() helper method using v3 API
3. src/Context/ThenStepDefinitions.php: Enhanced all comparison methods to show diffs

Example Output

When a comparison fails, users will now see:

--- Expected
+++ Actual
@@ -1,3 +1,3 @@
 Hello World
-This is a test
+This is different
 Third line

Quality Assurance

✅ No PHP syntax errors ✅ No security vulnerabilities ✅ All code review feedback addressed ✅ Proper error handling for JSON operations ✅ Full type hints added ✅ Compatible with PHP 7.2+

Ready for merge!

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Improve Behat output to include diffs on failed comparisons</issue_title> <issue_description>When Behat compares two elements and finds them to not match, it would be helpful for debugging purposes to have a diff available that shows the exact difference between the two elements, like in this example output:

The SebastianBergmann\Diff\Differ class is available and can be used for that.</issue_description>

<agent_instructions>https://github.com/Behat/Behat/pull/1532 might be useful as inspiration.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@swissspidy Looks like an upcoming Behat release will have better diffs out of the box, see https://github.com/Behat/Behat/pull/1532

Not in v3.16 yet, so have to wait for the next one.

Requires PHP 7.2+ though, see https://github.com/wp-cli/wp-cli-tests/pull/228

Alternatively we can copy that logic of course.</comment_new>

• Fixes wp-cli/wp-cli-tests#17

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