diff --git a/src/execution/__tests__/abstract-test.js b/src/execution/__tests__/abstract-test.js
index 2311fba97b..a4884fc7be 100644
--- a/src/execution/__tests__/abstract-test.js
+++ b/src/execution/__tests__/abstract-test.js
@@ -14,19 +14,27 @@ import {
   GraphQLUnionType,
 } from '../../type/definition';
 
+import { buildSchema } from '../../utilities/buildASTSchema';
+
 import { executeSync, execute } from '../execute';
 
-async function executeQuery(args: {| schema: GraphQLSchema, query: string |}) {
-  const { schema, query } = args;
+async function executeQuery(args: {|
+  schema: GraphQLSchema,
+  query: string,
+  rootValue?: mixed,
+|}) {
+  const { schema, query, rootValue } = args;
   const document = parse(query);
   const result = executeSync({
     schema,
     document,
+    rootValue,
     contextValue: { async: false },
   });
   const asyncResult = await execute({
     schema,
     document,
+    rootValue,
     contextValue: { async: true },
   });
 
@@ -752,4 +760,134 @@ describe('Execute: Handles execution of abstract types', () => {
       ],
     });
   });
+
+  it('resolve Union type using __typename on source object', async () => {
+    const schema = buildSchema(`
+      type Query {
+        pets: [Pet]
+      }
+
+      union Pet = Cat | Dog
+
+      type Cat {
+        name: String
+        meows: Boolean
+      }
+
+      type Dog {
+        name: String
+        woofs: Boolean
+      }
+    `);
+
+    const query = `
+      {
+        pets {
+          name
+          ... on Dog {
+            woofs
+          }
+          ... on Cat {
+            meows
+          }
+        }
+      }
+    `;
+
+    const rootValue = {
+      pets: [
+        {
+          __typename: 'Dog',
+          name: 'Odie',
+          woofs: true,
+        },
+        {
+          __typename: 'Cat',
+          name: 'Garfield',
+          meows: false,
+        },
+      ],
+    };
+
+    expect(await executeQuery({ schema, query, rootValue })).to.deep.equal({
+      data: {
+        pets: [
+          {
+            name: 'Odie',
+            woofs: true,
+          },
+          {
+            name: 'Garfield',
+            meows: false,
+          },
+        ],
+      },
+    });
+  });
+
+  it('resolve Interface type using __typename on source object', async () => {
+    const schema = buildSchema(`
+      type Query {
+        pets: [Pet]
+      }
+
+      interface Pet {
+        name: String
+        }
+
+      type Cat implements Pet {
+        name: String
+        meows: Boolean
+      }
+
+      type Dog implements Pet {
+        name: String
+        woofs: Boolean
+      }
+    `);
+
+    const query = `
+      {
+        pets {
+          name
+          ... on Dog {
+            woofs
+          }
+          ... on Cat {
+            meows
+          }
+        }
+      }
+    `;
+
+    const rootValue = {
+      pets: [
+        {
+          __typename: 'Dog',
+          name: 'Odie',
+          woofs: true,
+        },
+        {
+          __typename: 'Cat',
+          name: 'Garfield',
+          meows: false,
+        },
+      ],
+    };
+
+    expect(await executeQuery({ schema, query, rootValue })).to.deep.equal({
+      data: {
+        pets: [
+          {
+            name: 'Odie',
+            woofs: true,
+          },
+          {
+            name: 'Garfield',
+            meows: false,
+          },
+        ],
+      },
+    });
+  });
 });
diff --git a/src/utilities/__tests__/buildASTSchema-test.js b/src/utilities/__tests__/buildASTSchema-test.js
index f2a92c96a5..f364e311dd 100644
--- a/src/utilities/__tests__/buildASTSchema-test.js
+++ b/src/utilities/__tests__/buildASTSchema-test.js
@@ -505,129 +505,6 @@ describe('Schema Builder', () => {
     expect(errors).to.have.lengthOf.above(0);
   });
 
-  it('Specifying Union type using __typename', () => {
-    const schema = buildSchema(`
-      type Query {
-        fruits: [Fruit]
-      }
-
-      union Fruit = Apple | Banana
-
-      type Apple {
-        color: String
-      }
-
-      type Banana {
-        length: Int
-      }
-    `);
-
-    const source = `
-      {
-        fruits {
-          ... on Apple {
-            color
-          }
-          ... on Banana {
-            length
-          }
-        }
-      }
-    `;
-
-    const rootValue = {
-      fruits: [
-        {
-          color: 'green',
-          __typename: 'Apple',
-        },
-        {
-          length: 5,
-          __typename: 'Banana',
-        },
-      ],
-    };
-
-    expect(graphqlSync({ schema, source, rootValue })).to.deep.equal({
-      data: {
-        fruits: [
-          {
-            color: 'green',
-          },
-          {
-            length: 5,
-          },
-        ],
-      },
-    });
-  });
-
-  it('Specifying Interface type using __typename', () => {
-    const schema = buildSchema(`
-      type Query {
-        characters: [Character]
-      }
-
-      interface Character {
-        name: String!
-      }
-
-      type Human implements Character {
-        name: String!
-        totalCredits: Int
-      }
-
-      type Droid implements Character {
-        name: String!
-        primaryFunction: String
-      }
-    `);
-
-    const source = `
-      {
-        characters {
-          name
-          ... on Human {
-            totalCredits
-          }
-          ... on Droid {
-            primaryFunction
-          }
-        }
-      }
-    `;
-
-    const rootValue = {
-      characters: [
-        {
-          name: 'Han Solo',
-          totalCredits: 10,
-          __typename: 'Human',
-        },
-        {
-          name: 'R2-D2',
-          primaryFunction: 'Astromech',
-          __typename: 'Droid',
-        },
-      ],
-    };
-
-    expect(graphqlSync({ schema, source, rootValue })).to.deep.equal({
-      data: {
-        characters: [
-          {
-            name: 'Han Solo',
-            totalCredits: 10,
-          },
-          {
-            name: 'R2-D2',
-            primaryFunction: 'Astromech',
-          },
-        ],
-      },
-    });
-  });
-
   it('Custom Scalar', () => {
     const sdl = dedent`
       scalar CustomScalar