Add integration tests for custom directives

These tests verify that the query plan includes custom
directives in requests to underlying services.

They also ensure that validation errors are as expected
when services define custom directives in an invalid way.

packages/apollo-gateway/src/__tests__/integration/custom-directives.test.ts

@@ -0,0 +1,104 @@
+import gql from 'graphql-tag';
+import { execute } from '../execution-utils';
+
+import * as accounts from '../__fixtures__/schemas/accounts';
+import * as books from '../__fixtures__/schemas/books';
+import * as inventory from '../__fixtures__/schemas/inventory';
+import * as product from '../__fixtures__/schemas/product';
+import * as reviews from '../__fixtures__/schemas/reviews';
+
+import { astSerializer, queryPlanSerializer } from '../../snapshotSerializers';
+
+expect.addSnapshotSerializer(astSerializer);
+expect.addSnapshotSerializer(queryPlanSerializer);
+
+describe('custom executable directives', () => {
+  it('passes directives along in requests to underlying services', async () => {
+    const query = gql`
+      query GetReviewers {
+        topReviews {
+          body @stream
+        }
+      }
+    `;
+
+    const { data, errors, queryPlan } = await execute(
+      [accounts, books, inventory, product, reviews],
+      {
+        query,
+      },
+    );
+
+    expect(errors).toBeUndefined();
+    expect(queryPlan).toCallService('reviews');
+    expect(queryPlan).toMatchInlineSnapshot(`
+      QueryPlan {
+        Fetch(service: "reviews") {
+          {
+            topReviews {
+              body @stream
+            }
+          }
+        },
+      }
+    `);
+  });
+
+  it("returns validation errors when directives aren't present across all services", async () => {
+    const invalidService = {
+      name: 'invalidService',
+      typeDefs: gql`
+        directive @invalid on QUERY
+      `,
+    };
+
+    const query = gql`
+      query GetReviewers {
+        topReviews {
+          body @stream
+        }
+      }
+    `;
+
+    expect(
+      execute([accounts, books, inventory, product, reviews, invalidService], {
+        query,
+      }),
+    ).rejects.toThrowErrorMatchingInlineSnapshot(`
+"[@stream] -> Custom directives must be implemented in every service. The following services do not implement the @stream directive: invalidService.
+
+[@invalid] -> Custom directives must be implemented in every service. The following services do not implement the @invalid directive: accounts, books, inventory, product, reviews."
+`);
+  });
+
+  it("returns validation errors when directives aren't identical across all services", async () => {
+    const invalidService = {
+      name: 'invalid',
+      typeDefs: gql`
+        directive @stream on QUERY
+      `,
+    };
+
+    const query = gql`
+      query GetReviewers {
+        topReviews {
+          body @stream
+        }
+      }
+    `;
+
+    expect(
+      execute([accounts, books, inventory, product, reviews, invalidService], {
+        query,
+      }),
+    ).rejects.toThrowErrorMatchingInlineSnapshot(`
+"[@stream] -> custom directives must be defined identically across all services. See below for a list of current implementations:
+	accounts: directive @stream on FIELD
+	books: directive @stream on FIELD
+	inventory: directive @stream on FIELD
+	product: directive @stream on FIELD
+	reviews: directive @stream on FIELD
+	invalid: directive @stream on QUERY"
+`);
+  });
+});