Make dispatchQueues errors more readable

Author: lordthorzonus

src/DataLoader.php

@@ -191,12 +191,10 @@ private function dispatchQueueBatch($batch)
         /** @var Promise $batchPromise */
         $batchPromise = $batchLoadFunction($keys);
 
-        if (! $batchPromise || ! \is_callable([$batchPromise, 'then'])) {
-            return $this->handleFailedDispatch($batch, new DataLoaderException(
-                self::class . ' must be constructed with a function which accepts ' .
-                'an array of keys and returns a Promise which resolves to an array of values ' .
-                \sprintf('not return a Promise: %s.', \gettype($batchPromise))
-            ));
+        try {
+            $this->validateBatchPromise($batchPromise);
+        } catch (DataLoaderException $exception) {
+            return $this->handleFailedDispatch($batch, $exception);
         }
 
         $batchPromise->then(
@@ -262,7 +260,7 @@ private function handleFailedDispatch(array $batch, \Exception $error)
     }
 
     /**
-     * Validates the batch promises output.
+     * Validates the batch promise's output.
      *
      * @param array $values Values from resolved promise.
      * @param array $keys Keys which the DataLoaders load was called with
@@ -286,4 +284,22 @@ private function validateBatchPromiseOutput($values, $keys)
             );
         }
     }
+
+    /**
+     * Validates the batch promise returned from the batch load function.
+     *
+     * @param $batchPromise
+     *
+     * @throws DataLoaderException
+     */
+    private function validateBatchPromise($batchPromise)
+    {
+        if (! $batchPromise || ! \is_callable([$batchPromise, 'then'])) {
+            throw new DataLoaderException(
+                self::class . ' must be constructed with a function which accepts ' .
+                'an array of keys and returns a Promise which resolves to an array of values ' .
+                \sprintf('the function returned %s.', \gettype($batchPromise))
+            );
+        }
+    }
 }

tests/Unit/DataLoaderAbuseTest.php

@@ -74,7 +74,7 @@ public function batch_function_must_return_a_promise_not_null()
 
         /** @var DataLoaderException $exception */
         $expectedExceptionMessage = 'leinonen\DataLoader\DataLoader must be constructed with a function which accepts an array of keys '
-            . 'and returns a Promise which resolves to an array of values not return a Promise: NULL.';
+            . 'and returns a Promise which resolves to an array of values the function returned NULL.';
         $this->assertInstanceOf(DataLoaderException::class, $exception);
         $this->assertSame($expectedExceptionMessage, $exception->getMessage());
     }
@@ -98,7 +98,7 @@ public function batch_function_must_return_a_promise_not_a_array()
 
         /** @var DataLoaderException $exception */
         $expectedExceptionMessage = 'leinonen\DataLoader\DataLoader must be constructed with a function which accepts an array of keys '
-            . 'and returns a Promise which resolves to an array of values not return a Promise: array.';
+            . 'and returns a Promise which resolves to an array of values the function returned array.';
         $this->assertInstanceOf(DataLoaderException::class, $exception);
         $this->assertSame($expectedExceptionMessage, $exception->getMessage());
     }
@@ -122,7 +122,7 @@ public function batch_function_must_return_a_promise_not_a_value()
 
         /** @var DataLoaderException $exception */
         $expectedExceptionMessage = 'leinonen\DataLoader\DataLoader must be constructed with a function which accepts an array of keys '
-            . 'and returns a Promise which resolves to an array of values not return a Promise: integer.';
+            . 'and returns a Promise which resolves to an array of values the function returned integer.';
         $this->assertInstanceOf(DataLoaderException::class, $exception);
         $this->assertSame($expectedExceptionMessage, $exception->getMessage());
     }
@@ -147,7 +147,7 @@ function ($keys) {
 
         /** @var DataLoaderException $exception */
         $expectedExceptionMessage = 'leinonen\DataLoader\DataLoader must be constructed with a function which accepts an array of keys '
-            . 'and returns a Promise which resolves to an array of values not return a Promise: object.';
+            . 'and returns a Promise which resolves to an array of values the function returned object.';
         $this->assertInstanceOf(DataLoaderException::class, $exception);
         $this->assertSame($expectedExceptionMessage, $exception->getMessage());
     }