added a promises test

Author: nginnever

test/files.js

@@ -109,6 +109,23 @@ module.exports = (common) => {
             expect(err).to.not.exist
           })
         })
+
+        it('returns error on invalid key', (done) => {
+          const hash = 'somethingNotMultihash'
+          ipfs.cat(hash)
+          .then((stream) => {})
+          .catch((err) => {
+            expect(err).to.exist
+            const errString = err.toString()
+            if (errString === 'Error: invalid ipfs ref path') {
+              expect(err.toString()).to.contain('Error: invalid ipfs ref path')
+            }
+            if (errString === 'Error: Invalid Key') {
+              expect(err.toString()).to.contain('Error: Invalid Key')
+            }
+            done()
+          })
+        })
       })
     })
   })