Add failing test

tests/phpunit/MergePluginTest.php

@@ -1572,6 +1572,27 @@ function ($args, $root) {
         $this->triggerPlugin($root->reveal(), $dir, $fireInit);
     }
 
+    public function testGitHubIssue222()
+    {
+        $that = $this;
+        $dir = $this->fixtureDir(__FUNCTION__);
+
+        $root = $this->rootFromJson("{$dir}/composer.json");
+        $root->setRequires(Argument::type('array'))->will(
+            function ($args) use ($that) {
+                $requires = $args[0];
+                $that->assertCount(2, $requires);
+                $that->assertArrayHasKey('symfony/yaml', $requires);
+
+                $that->assertEquals(
+                    '5.3.6',
+                    $requires['symfony/yaml']->getPrettyConstraint()
+                );
+            }
+        );
+        $this->triggerPlugin($root->reveal(), $dir);
+    }
+
     /**
      * Generic provider for tests that should be tried with and without an
      * INIT event.

tests/phpunit/fixtures/testGitHubIssue222/composer-extra.json

@@ -0,0 +1,5 @@
+{
+	"require": {
+		"symfony/yaml": "5.3.6"
+	}
+}

tests/phpunit/fixtures/testGitHubIssue222/composer.json

@@ -0,0 +1,16 @@
+{
+	"require": {
+		"wikimedia/composer-merge-plugin": "dev-master"
+	},
+	"require-dev": {
+		"symfony/yaml": "~3.4|~5.1"
+	},
+	"extra": {
+		"merge-plugin": {
+			"include": [
+				"composer.local.json"
+			],
+			"merge-dev": false
+		}
+	}
+}

tests/phpunit/fixtures/testGitHubIssue222/composer.local.json

@@ -0,0 +1,9 @@
+{
+        "extra": {
+                "merge-plugin": {
+                        "include": [
+                                "composer-extra.json"
+                        ]
+                }
+        }
+}