OutputMatches Assertion

The OutputMatches assertion checks that the output matches a regular expression pattern.

Syntax

```php
echo date('Y');
```
<!-- doctest-matches: /^\d{4}$/ -->

How It Works

1. The code block executes and its output is captured
2. The pattern is used with preg_match() against the actual output
3. If the regex is invalid, the assertion fails with a descriptive error

Pattern Format

Patterns must include delimiters, just like PHP's preg_match():

```php
echo 'abc123';
```
<!-- doctest-matches: /^[a-z]+\d+$/ -->

```php
echo 'Hello World';
```
<!-- doctest-matches: /hello world/i -->

When to Use

• When the output has a known structure but variable content
• When you need more precision than OutputContains but more flexibility than Output
• When validating formats like dates, UUIDs, or version strings

Examples

Validate email format

echo 'user@example.com';

Match a version string

echo '2.1.0';

TIP

For common dynamic patterns like dates, UUIDs, and integers, consider using wildcards with the Output assertion instead. They're more readable.