handle error condition when client is offline

[marcosh]

currently several tests fail if the machine executing the tests is offline

  ✗ sets data correctly with no option:                                                                                                                                                                                                      
                                                                                                                                                                                                                                             
  test timed out after 2000ms                                                                                                                                                                                                                
  ✗ sets data correctly with merge option:

  test timed out after 2000ms                              
  ✗ sets data correctly with mergeFields option:

  test timed out after 2000ms                              
[2020-03-18T17:08:12.803Z]  @firebase/firestore: Firestore (7.9.2): Could not reach Cloud Firestore backend. Connection failed 1 times. Most recent error: FirebaseError: [code=unavailable]: 14 UNAVAILABLE: DNS resolution failed
This typically indicates that your device does not have a healthy Internet connection at the moment. The client will operate in offline mode until it is able to successfully connect to the backend.
  ✗ gets existing data correctly with default options:

  test timed out after 2000ms                              
  ✗ gets existing data correctly with cache options:

  test timed out after 2000ms                              
[2020-03-18T17:08:16.804Z]  @firebase/firestore: Firestore (7.9.2): Could not reach Cloud Firestore backend. Connection failed 1 times. Most recent error: FirebaseError: [code=unavailable]: 14 UNAVAILABLE: DNS resolution failed
This typically indicates that your device does not have a healthy Internet connection at the moment. The client will operate in offline mode until it is able to successfully connect to the backend.
(node:6376) UnhandledPromiseRejectionWarning: FirebaseError: Failed to get document from server. (However, this document does exist in the local cache. Run again without setting source to "server" to retrieve the cached document.)
    at new FirestoreError (/home/marcosh/projects/statebox/purescript-firestore/node_modules/@firebase/firestore/dist/index.node.cjs.js:348:28)
    at Object.next (/home/marcosh/projects/statebox/purescript-firestore/node_modules/@firebase/firestore/dist/index.node.cjs.js:21990:28)
    at next (/home/marcosh/projects/statebox/purescript-firestore/node_modules/@firebase/firestore/dist/index.node.cjs.js:21937:30)
    at Timeout._onTimeout (/home/marcosh/projects/statebox/purescript-firestore/node_modules/@firebase/firestore/dist/index.node.cjs.js:20178:21)
    at listOnTimeout (internal/timers.js:531:17)
    at processTimers (internal/timers.js:475:7)
(node:6376) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)                                                 
(node:6376) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
  ✗ gets existing data correctly with server options:

  test timed out after 2000ms                              
[2020-03-18T17:08:18.785Z]  @firebase/firestore: Firestore (7.9.2): Could not reach Cloud Firestore backend. Connection failed 1 times. Most recent error: FirebaseError: [code=unavailable]: 14 UNAVAILABLE: DNS resolution failed
This typically indicates that your device does not have a healthy Internet connection at the moment. The client will operate in offline mode until it is able to successfully connect to the backend.
  ✗ gets data with was not set before:

  Failed to get document because the client is offline.
[2020-03-18T17:08:18.841Z]  @firebase/firestore: Firestore (7.9.2): Could not reach Cloud Firestore backend. Connection failed 1 times. Most recent error: FirebaseError: [code=unavailable]: 14 UNAVAILABLE: DNS resolution failed
This typically indicates that your device does not have a healthy Internet connection at the moment. The client will operate in offline mode until it is able to successfully connect to the backend.
  ✗ sets and gets data correctly:

  test timed out after 2000ms                              
[2020-03-18T17:08:20.837Z]  @firebase/firestore: Firestore (7.9.2): Could not reach Cloud Firestore backend. Connection failed 1 times. Most recent error: FirebaseError: [code=unavailable]: 14 UNAVAILABLE: DNS resolution failed
This typically indicates that your device does not have a healthy Internet connection at the moment. The client will operate in offline mode until it is able to successfully connect to the backend.
  ✗ sets and gets data correctly with estimate timestamp:

  test timed out after 2000ms                              
[2020-03-18T17:08:22.849Z]  @firebase/firestore: Firestore (7.9.2): Could not reach Cloud Firestore backend. Connection failed 1 times. Most recent error: FirebaseError: [code=unavailable]: 14 UNAVAILABLE: DNS resolution failed
This typically indicates that your device does not have a healthy Internet connection at the moment. The client will operate in offline mode until it is able to successfully connect to the backend.
  ✗ sets and gets data correctly with previous timestamp:

  test timed out after 2000ms