Ensure input-provider elements of collections merge inputs correctly

As reported in #78, if you compose an input filter provider fieldset as
a target element of a collection in order to allow providing a default
fieldset for the collection, input provider elements composed by the
input filter provider fieldset were not being merged correctly into the
input filter.

This patch checks to see if the fieldset's input filter represents a
collection, and, if so, will check its own composed input filter for the
element and merge it if found.

src/Form.php

@@ -792,6 +792,19 @@ public function attachInputFilterDefaults(InputFilterInterface $inputFilter, Fie
                         $inputFilter->replace($input, $name);
                         continue;
                     }
+
+                    // If we are dealing with a collection input filter, check
+                    // the input filter it composes for an element of the same
+                    // name as was done above.
+                    if ($inputFilter instanceof CollectionInputFilter
+                        && $inputFilter->getInputFilter()->has($name)
+                        && $inputFilter->getInputFilter() instanceof ReplaceableInputInterface
+                    ) {
+                        $collectionInputFilter = $inputFilter->getInputFilter();
+                        $input->merge($collectionInputFilter->get($name));
+                        $collectionInputFilter->replace($input, $name);
+                        continue;
+                    }
                 }
 
                 // Add element input filter to CollectionInputFilter

test/Integration/FormCreatesCollectionInputFilterTest.php

@@ -17,11 +17,13 @@ class FormCreatesCollectionInputFilterTest extends TestCase
     public static function assertValidatorFound($class, array $validators, $message = null)
     {
         $message = $message ?: sprintf('Failed to find validator of type %s in validator list', $class);
-        foreach ($validators as $validator) {
+        foreach ($validators as $instance) {
+            $validator = $instance['instance'];
             if ($validator instanceof $class) {
                 return true;
             }
         }
+        var_export($validators);
         self::fail($message);
     }
 
@@ -63,7 +65,7 @@ public function testCollectionInputFilterContainsExpectedValidators()
         $this->assertCount(3, $validators);
         $this->assertValidatorFound(Validator\StringLength::class, $validators);
         $this->assertValidatorFound(Validator\Date::class, $validators);
-        $this->assertValidatorFound(Validator\Step::class, $validators);
+        $this->assertValidatorFound(Validator\DateStep::class, $validators);
 
         return $form;
     }