Throw exception if description field doesnt exist

Author: dantleech

lib/Extension/Core/Stage/Aggregator/DescribeAggregator.php

@@ -26,6 +26,13 @@ public function __invoke(): Generator
                     $samples[$hash][$field] = [];
                 }
 
+                if (false === isset($data[$field])) {
+                    throw new InvalidArgumentException(sprintf(
+                        'Field "%s" does not exist in data with fields "%s"',
+                        $field, implode('", "', array_keys($data))
+                    ));
+                }
+
                 $samples[$hash][$field][] = $data[$field];
             }
 

tests/Unit/Extension/Core/Stage/Aggregator/DescribeAggregatorTest.php

@@ -3,6 +3,7 @@
 namespace PhpBench\Pipeline\Tests\Unit\Extension\Core\Stage\Aggregator;
 
 use PhpBench\Pipeline\Tests\Unit\Extension\Core\CoreTestCase;
+use InvalidArgumentException;
 
 class DescribeAggregatorTest extends CoreTestCase
 {
@@ -77,4 +78,22 @@ public function testItGroupsByMultipleColumns()
         $this->assertArrayHasKey('two, one', $result);
         $this->assertArrayHasKey('three, three', $result);
     }
+
+    public function testThrowsExceptionIfGroupByFieldDoesntExist()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Field "tie" does not exist in data with fields "one", "two", "time"');
+        $this->pipeline()
+            ->stage(function () {
+                yield;
+                yield ['one' => 'one', 'two' => 'two', 'time' => 10];
+            })
+            ->stage('aggregator/describe', [
+                'group_by' => ['one' ],
+                'describe' => ['tie'],
+            ])
+            ->run();
+
+    }
+
 }