Test: Uncaptured errors in source event stream.

Added a test to illustrate a broken issue and potentially underspecified in spec:

If a source event stream emits an *error* instead of an *event*, then that error is passing up through the whole stack and throwing at the consumer of the response event stream. That's very likely not what we want. I have a proposal in this test case for what should happen in that case, similar to what would happen if an error occurred during during the second step of executing an event from the source stream.

src/subscription/__tests__/asyncIteratorReject-test.js

@@ -0,0 +1,41 @@
+/**
+ *  Copyright (c) 2017, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import asyncIteratorReject from '../asyncIteratorReject';
+
+describe('asyncIteratorReject', () => {
+
+  it('creates a failing async iterator', async () => {
+    const error = new Error('Oh no, Mr. Bill!');
+    const iter = asyncIteratorReject(error);
+
+    let caughtError;
+    try {
+      await iter.next();
+    } catch (thrownError) {
+      caughtError = thrownError;
+    }
+    expect(caughtError).to.equal(error);
+
+    expect(await iter.next()).to.deep.equal({ done: true, value: undefined });
+  });
+
+  it('can be closed before failing', async () => {
+    const error = new Error('Oh no, Mr. Bill!');
+    const iter = asyncIteratorReject(error);
+
+    // Close iterator
+    expect(await iter.return()).to.deep.equal({ done: true, value: undefined });
+
+    expect(await iter.next()).to.deep.equal({ done: true, value: undefined });
+  });
+});

src/subscription/__tests__/asyncIteratorResolve-test.js

@@ -0,0 +1,34 @@
+/**
+ *  Copyright (c) 2017, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+import { expect } from 'chai';
+import { describe, it } from 'mocha';
+
+import asyncIteratorResolve from '../asyncIteratorResolve';
+
+describe('asyncIteratorResolve', () => {
+
+  it('creates a failing async iterator', async () => {
+    const value = 'Hello world!';
+    const iter = asyncIteratorResolve(value);
+
+    expect(await iter.next()).to.deep.equal({ done: false, value });
+    expect(await iter.next()).to.deep.equal({ done: true, value: undefined });
+  });
+
+  it('can be closed before failing', async () => {
+    const value = 'Hello world!';
+    const iter = asyncIteratorResolve(value);
+
+    // Close iterator
+    expect(await iter.return()).to.deep.equal({ done: true, value: undefined });
+
+    expect(await iter.next()).to.deep.equal({ done: true, value: undefined });
+  });
+});

src/subscription/__tests__/subscribe-test.js

@@ -77,7 +77,7 @@ describe('Subscribe', () => {
     subscription: SubscriptionType
   });
 
-  function createSubscription(pubsub, schema = emailSchema) {
+  function createSubscription(pubsub, schema = emailSchema, ast) {
     const data = {
       inbox: {
         emails: [
@@ -105,7 +105,7 @@ describe('Subscribe', () => {
       });
     }
 
-    const ast = parse(`
+    const defaultAst = parse(`
       subscription ($priority: Int = 0) {
         importantEmail(priority: $priority) {
           email {
@@ -126,7 +126,7 @@ describe('Subscribe', () => {
       sendImportantEmail,
       subscription: subscribe(
         schema,
-        ast,
+        ast || defaultAst,
         data
       ),
     };
@@ -545,22 +545,22 @@ describe('Subscribe', () => {
     });
   });
 
-  it('invalid query should result in error', async () => {
-    const invalidAST = parse(`
+  it('unknown field should result in closed subscription', async () => {
+    const ast = parse(`
       subscription {
-        invalidField
+        unknownField
       }
     `);
 
-    expect(() => {
-      subscribe(
-        emailSchema,
-        invalidAST,
-      );
-    }).to.throw('This subscription is not defined by the schema.');
+    const pubsub = new EventEmitter();
+
+    const { subscription } = createSubscription(pubsub, emailSchema, ast);
+
+    const payload = await subscription.next();
+    expect(payload).to.deep.equal({ done: true, value: undefined });
   });
 
-  it('throws when subscription definition doesnt return iterator', () => {
+  it('fails when subscription definition doesnt return iterator', async () => {
     const invalidEmailSchema = new GraphQLSchema({
       query: QueryType,
       subscription: new GraphQLObjectType({
@@ -574,18 +574,19 @@ describe('Subscribe', () => {
       })
     });
 
-    const ast = parse(`
-      subscription {
-        importantEmail
-      }
-    `);
+    const pubsub = new EventEmitter();
 
-    expect(() => {
-      subscribe(
-        invalidEmailSchema,
-        ast
-      );
-    }).to.throw('Subscription must return Async Iterable.');
+    const { subscription } = createSubscription(pubsub, invalidEmailSchema);
+
+    let caughtError;
+    try {
+      await subscription.next();
+    } catch (thrownError) {
+      caughtError = thrownError;
+    }
+    expect(
+      caughtError && caughtError.message
+    ).to.equal('Subscription must return Async Iterable. Returned: test');
   });
 
   it('expects to have subscribe on type definition with iterator', () => {
@@ -617,33 +618,196 @@ describe('Subscribe', () => {
     }).not.to.throw();
   });
 
-  it('should handle error thrown by subscribe method', () => {
-    const invalidEmailSchema = new GraphQLSchema({
+  it('should report error thrown by subscribe function', async () => {
+    const erroringEmailSchema = emailSchemaWithSubscribeFn(
+      function importantEmail() {
+        throw new Error('test error');
+      }
+    );
+
+    const subscription = subscribe(
+      erroringEmailSchema,
+      parse(`
+        subscription {
+          importantEmail
+        }
+      `)
+    );
+
+    const result = await subscription.next();
+
+    expect(result).to.deep.equal({
+      done: false,
+      value: {
+        errors: [
+          {
+            message: 'test error',
+            locations: [ { line: 3, column: 11 } ],
+            path: [ 'importantEmail' ]
+          }
+        ]
+      }
+    });
+
+    expect(
+      await subscription.next()
+    ).to.deep.equal({ value: undefined, done: true });
+  });
+
+  it('should report error returned by subscribe function', async () => {
+    const erroringEmailSchema = emailSchemaWithSubscribeFn(
+      function importantEmail() {
+        return new Error('test error');
+      }
+    );
+
+    const subscription = subscribe(
+      erroringEmailSchema,
+      parse(`
+        subscription {
+          importantEmail
+        }
+      `)
+    );
+
+    const result = await subscription.next();
+
+    expect(result).to.deep.equal({
+      done: false,
+      value: {
+        errors: [
+          {
+            message: 'test error',
+            locations: [ { line: 3, column: 11 } ],
+            path: [ 'importantEmail' ]
+          }
+        ]
+      }
+    });
+
+    expect(
+      await subscription.next()
+    ).to.deep.equal({ value: undefined, done: true });
+  });
+
+  it('should handle error during execuction of source event', async () => {
+    const erroringEmailSchema = new GraphQLSchema({
       query: QueryType,
       subscription: new GraphQLObjectType({
         name: 'Subscription',
         fields: {
           importantEmail: {
             type: GraphQLString,
-            subscribe: () => {
-              throw new Error('test error');
+            resolve(event) {
+              if (event === 'Goodbye') {
+                throw new Error('Never leave.');
+              }
+              return event;
+            },
+            subscribe: async function* importantEmail() {
+              yield 'Hello';
+              yield 'Goodbye';
             },
           },
         },
       })
     });
 
-    const ast = parse(`
-      subscription {
-        importantEmail
+    const subscription = subscribe(
+      erroringEmailSchema,
+      parse(`
+        subscription {
+          importantEmail
+        }
+      `)
+    );
+
+    const payload1 = await subscription.next();
+    expect(payload1).to.jsonEqual({
+      done: false,
+      value: {
+        data: {
+          importantEmail: 'Hello'
+        }
       }
-    `);
+    });
 
-    expect(() => {
-      subscribe(
-        invalidEmailSchema,
-        ast
-      );
-    }).to.throw('test error');
+    const payload2 = await subscription.next();
+    expect(payload2).to.jsonEqual({
+      done: false,
+      value: {
+        errors: [
+          {
+            message: 'Never leave.',
+            locations: [ { line: 3, column: 11 } ],
+            path: [ 'importantEmail' ],
+          }
+        ],
+        data: {
+          importantEmail: null,
+        }
+      }
+    });
+  });
+
+  function emailSchemaWithSubscribeFn(subscribeFn) {
+    return new GraphQLSchema({
+      query: QueryType,
+      subscription: new GraphQLObjectType({
+        name: 'Subscription',
+        fields: {
+          importantEmail: {
+            type: GraphQLString,
+            resolve(event) {
+              return event;
+            },
+            subscribe: subscribeFn,
+          },
+        },
+      })
+    });
+  }
+
+  it('should pass through error thrown in source event stream', async () => {
+    const erroringEmailSchema = emailSchemaWithSubscribeFn(
+      async function* importantEmail() {
+        yield 'Hello';
+        throw new Error('test error');
+      }
+    );
+
+    const subscription = subscribe(
+      erroringEmailSchema,
+      parse(`
+        subscription {
+          importantEmail
+        }
+      `)
+    );
+
+    const payload1 = await subscription.next();
+    expect(payload1).to.jsonEqual({
+      done: false,
+      value: {
+        data: {
+          importantEmail: 'Hello'
+        }
+      }
+    });
+
+    let expectedError;
+    try {
+      await subscription.next();
+    } catch (error) {
+      expectedError = error;
+    }
+
+    expect(expectedError).to.deep.equal(new Error('test error'));
+
+    const payload2 = await subscription.next();
+    expect(payload2).to.jsonEqual({
+      done: true,
+      value: undefined
+    });
   });
 });