[ios, macos] Fixed MGLMapSnapshotter test crash

Fixed a crash in MGLDocumentationExampleTests caused by an asynchronous snapshot call that the test wasn’t waiting on, compounded by the use of a style that requires an access token (as opposed to the one-liner style that uses no remote resources. Employed some Swiftisms to fulfill expectations without making the example code look weird.

2 files changed, 33 insertions, 10 deletions

diff --git a/platform/darwin/src/MGLMapSnapshotter.h b/platform/darwin/src/MGLMapSnapshotter.h
index fc68204a7d..426ab1bb00 100644
--- a/platform/darwin/src/MGLMapSnapshotter.h
+++ b/platform/darwin/src/MGLMapSnapshotter.h
@@ -145,11 +145,11 @@ typedef void (^MGLMapSnapshotCompletionHandler)(MGLMapSnapshot* _Nullable snapsh
  
  let snapshotter = MGLMapSnapshotter(options: options)
  snapshotter.start { (snapshot, error) in
-     if error != nil {
-         // error handler
-     } else {
-         // image handler
+     if let error = error {
+         fatalError(error.localizedDescription)
      }
+     
+     image = snapshot?.image
  }
  ```
  */
diff --git a/platform/darwin/test/MGLDocumentationExampleTests.swift b/platform/darwin/test/MGLDocumentationExampleTests.swift
index 8762af9ba4..668e5f57f8 100644
--- a/platform/darwin/test/MGLDocumentationExampleTests.swift
+++ b/platform/darwin/test/MGLDocumentationExampleTests.swift
@@ -27,11 +27,11 @@ import Mapbox
 class MGLDocumentationExampleTests: XCTestCase, MGLMapViewDelegate {
     var mapView: MGLMapView!
     var styleLoadingExpectation: XCTestExpectation!
+    static let styleURL = Bundle(for: MGLDocumentationExampleTests.self).url(forResource: "one-liner", withExtension: "json")!
 
     override func setUp() {
         super.setUp()
-        let styleURL = Bundle(for: MGLDocumentationExampleTests.self).url(forResource: "one-liner", withExtension: "json")
-        mapView = MGLMapView(frame: CGRect(x: 0, y: 0, width: 256, height: 256), styleURL: styleURL)
+        mapView = MGLMapView(frame: CGRect(x: 0, y: 0, width: 256, height: 256), styleURL: MGLDocumentationExampleTests.styleURL)
         mapView.delegate = self
         styleLoadingExpectation = expectation(description: "Map view should finish loading style")
         waitForExpectations(timeout: 1, handler: nil)
@@ -279,6 +279,27 @@ class MGLDocumentationExampleTests: XCTestCase, MGLMapViewDelegate {
     }
     
     func testMGLMapSnapshotter() {
+        let expectation = self.expectation(description: "MGLMapSnapshotter should produce a snapshot")
+        #if os(macOS)
+            var image: NSImage? {
+                didSet {
+                    expectation.fulfill()
+                }
+            }
+        #else
+            var image: UIImage? {
+                didSet {
+                    expectation.fulfill()
+                }
+            }
+        #endif
+        
+        class MGLStyle {
+            static func satelliteStreetsStyleURL() -> URL {
+                return MGLDocumentationExampleTests.styleURL
+            }
+        }
+        
         //#-example-code
         let camera = MGLMapCamera(lookingAtCenter: CLLocationCoordinate2D(latitude: 37.7184, longitude: -122.4365), fromDistance: 100, pitch: 20, heading: 0)
 
@@ -287,13 +308,15 @@ class MGLDocumentationExampleTests: XCTestCase, MGLMapViewDelegate {
 
         let snapshotter = MGLMapSnapshotter(options: options)
         snapshotter.start { (snapshot, error) in
-            if error != nil {
-                // error handler
-            } else {
-                // image handler
+            if let error = error {
+                fatalError(error.localizedDescription)
             }
+            
+            image = snapshot?.image
         }
         //#-end-example-code
+        
+        wait(for: [expectation], timeout: 1)
     }
     
     // For testMGLMapView().