test: add fragment variable test

Author: smkhalsa

packages/normalize/test/query_fragments/fragment_variables_test.dart

@@ -0,0 +1,73 @@
+import 'package:test/test.dart';
+import 'package:gql/language.dart';
+
+import 'package:normalize/normalize.dart';
+
+void main() {
+  group('Fragment Variables', () {
+    final fragment = parseString('''
+      fragment authorFragment on Author {
+        id
+        __typename
+        posts(first: \$first) {
+          id
+        __typename
+        }
+      }
+    ''');
+
+    final normalizedMap = {
+      'Post:123': {
+        'id': 123,
+        '__typename': 'Post',
+      },
+      'Author:1': {
+        'id': 1,
+        '__typename': 'Author',
+        'posts({"first":10})': [
+          {'\$ref': 'Post:123'}
+        ]
+      },
+    };
+
+    final response = {
+      '__typename': 'Author',
+      'id': 1,
+      'posts': [
+        {
+          'id': 123,
+          '__typename': 'Post',
+        }
+      ],
+    };
+
+    test('Produces correct normalized object', () {
+      final normalizedResult = {};
+      normalizeFragment(
+        read: (dataId) => normalizedResult[dataId],
+        write: (dataId, value) => normalizedResult[dataId] = value,
+        document: fragment,
+        data: response,
+        idFields: {'id': 1},
+        variables: {'first': 10},
+      );
+
+      expect(
+        normalizedResult,
+        equals(normalizedMap),
+      );
+    });
+
+    test('Produces correct nested data object', () {
+      expect(
+        denormalizeFragment(
+          document: fragment,
+          read: (dataId) => normalizedMap[dataId],
+          variables: {'first': 10},
+          idFields: {'id': 1},
+        ),
+        equals(response),
+      );
+    });
+  });
+}