Separate index objects for each analysis context.

pkg/analysis_server/test/services/index2/index2_test.dart

Index: pkg/analysis_server/test/services/index2/index2_test.dart
diff --git a/pkg/analysis_server/test/services/index2/index2_test.dart b/pkg/analysis_server/test/services/index2/index2_test.dart
index 5a9abb0e66c8927ff8efe05361c3a40dd88b62cc..a23d0c4fa84527293067e6d96b167dc1a605bc60 100644
--- a/pkg/analysis_server/test/services/index2/index2_test.dart
+++ b/pkg/analysis_server/test/services/index2/index2_test.dart
@@ -180,6 +180,29 @@ main(A a, p) {
     findLocationTest(locations, 'test); // p-ref-ur-q');
   }
 
+  test_indexUnit_nullUnit() async {
+    index.indexUnit(null);
+  }
+
+  test_indexUnit_nullUnitElement() async {
+    resolveTestUnit('');
+    testUnit.element = null;
+    index.indexUnit(testUnit);
+  }
+
+  test_removeContext() async {
+    _indexTestUnit('''
+class A {}
+''');
+    RegExp regExp = new RegExp(r'^A$');
+    expect(await index.getDefinedNames(regExp, IndexNameKind.topLevel),
+        hasLength(1));
+    // remove the context - no
+    index.removeContext(context);
+    expect(
+        await index.getDefinedNames(regExp, IndexNameKind.topLevel), isEmpty);
+  }
+
   /**
    * Assert that the given list of [locations] has a [Location] corresponding
    * to the [element].