Add test for handling partial data with error(s)

README.md

@@ -166,6 +166,70 @@ try {
 }
 ```
 
+## Partial responses
+
+A GraphQL query may respond with partial data accompanied by errors. In this case we will throw an error but the partial data will still be accessible through `error.data`
+
+```js
+const graphql = require('@octokit/graphql').defaults({
+  headers: {
+    authorization: `token secret123`
+  }
+})
+const query = `{
+  repository(name: "probot", owner: "probot") {
+    name
+    ref(qualifiedName: "master") {
+      target {
+        ... on Commit {
+          history(first: 25, after: "invalid cursor") {
+            nodes {
+              message
+            }
+          }
+        }
+      }
+    }
+  }
+}`
+
+try {
+  const result = await graphql(query)
+} catch (error) {
+  // server responds with
+  // { 
+  //   "data": { 
+  //     "repository": { 
+  //       "name": "probot", 
+  //       "ref": null 
+  //     } 
+  //   }, 
+  //   "errors": [ 
+  //     { 
+  //       "type": "INVALID_CURSOR_ARGUMENTS", 
+  //       "path": [ 
+  //         "repository", 
+  //         "ref", 
+  //         "target", 
+  //         "history" 
+  //       ], 
+  //       "locations": [ 
+  //         { 
+  //           "line": 7, 
+  //           "column": 11 
+  //         } 
+  //       ], 
+  //       "message": "`invalid cursor` does not appear to be a valid cursor." 
+  //     } 
+  //   ] 
+  // } 
+
+  console.log('Request failed:', error.request) // { query, variables: {}, headers: { authorization: 'token secret123' } }
+  console.log(error.message) // `invalid cursor` does not appear to be a valid cursor.
+  console.log(error.data) // { repository: { name: 'probot', ref: null } }
+}
+```
+
 ## Writing tests
 
 You can pass a replacement for [the built-in fetch implementation](https://github.com/bitinn/node-fetch) as `request.fetch` option. For example, using [fetch-mock](http://www.wheresrhys.co.uk/fetch-mock/) works great to write tests

lib/graphql.js

@@ -27,10 +27,10 @@ function graphql (request, query, options) {
 
   return request(requestOptions)
     .then(response => {
-      if (response.data.data) {
-        return response.data.data
+      if (response.data.errors) {
+        throw new GraphqlError(requestOptions, response)
       }
 
-      throw new GraphqlError(requestOptions, response)
+      return response.data.data
     })
 }

test/error-test.js

@@ -47,4 +47,64 @@ describe('errors', () => {
         expect(error.request.query).to.equal(query)
       })
   })
+
+  it('Should throw an error for a partial response accompanied by errors', () => {
+    const query = `{
+      repository(name: "probot", owner: "probot") {
+        name
+        ref(qualifiedName: "master") {
+          target {
+            ... on Commit {
+              history(first: 25, after: "invalid cursor") {
+                nodes {
+                  message
+                }
+              }
+            }
+          }
+        }
+      }
+    }`
+
+    const mockResponse = {
+      data: {
+        repository: {
+          name: 'probot',
+          ref: null
+        }
+      },
+      errors: [
+        {
+          type: 'INVALID_CURSOR_ARGUMENTS',
+          path: ['repository', 'ref', 'target', 'history'],
+          locations: [
+            {
+              line: 7,
+              column: 11
+            }
+          ],
+          message: '`invalid cursor` does not appear to be a valid cursor.'
+        }
+      ]
+    }
+
+    return graphql(query, {
+      headers: {
+        authorization: `token secret123`
+      },
+      request: {
+        fetch: fetchMock.sandbox()
+          .post('https://api.github.com/graphql', mockResponse)
+      }
+    })
+
+      .then(result => {
+        throw new Error('Should not resolve')
+      }).catch(error => {
+        expect(error.message).to.equal('`invalid cursor` does not appear to be a valid cursor.')
+        expect(error.errors).to.deep.equal(mockResponse.errors)
+        expect(error.request.query).to.equal(query)
+        expect(error.data).to.deep.equal(mockResponse.data)
+      })
+  })
 })