Debug Dump (// => dd())

The debug dump syntax lets you inspect expression values during test execution without affecting pass/fail results. It uses the same // => syntax as result comments, but with dd() as the expected value.

Syntax

$expression; // => dd()

The expression value is captured and displayed in the test output. The block always passes regardless of the value.

How It Works

1. The expression on the left side of // => dd() is evaluated
2. The result is captured using var_export()
3. The value is displayed in the test output with a dd marker
4. No comparison is made — the block passes as long as no runtime error occurs

When to Use

• Debugging — quickly inspect what an expression returns
• Exploring — understand unfamiliar code behavior
• Prototyping assertions — see the actual value before writing a // => assertion

Examples

Single dump

$x = 42; // => dd()

Multiple dumps in one block

$x = 1; // => dd()
$y = 2; // => dd()
$z = $x + $y; // => dd()

Mixed with assertions

Debug dumps can coexist with regular assertions in the same block. The assertions are checked normally, while the dumps just display values:

$x = 42; // => dd()
$y = 10; // => 10

Function calls

strtoupper("hello"); // => dd()

In group blocks

Debug dumps work in grouped blocks with shared state:

```php group="calc"
$base = 100; // => dd()
```

```php group="calc"
$result = $base * 1.2; // => dd()
echo $result;
```
<!-- doctest: 120 -->

Output Format

When running DocTest, debug dumps appear with a dd marker:

  :1 ✔ $x = 42; // => dd()
       dd $x = 42 => 42

The output is always shown regardless of verbosity level (-v, -vv).

Comparison with Result Comment

Feature	// => value	// => dd()
Compares value	Yes	No
Affects pass/fail	Yes	No
Shows value in output	Only with -v	Always
Use case	Verify correctness	Inspect & debug