Added some tests after the fact for flutter#17499.

Author: gaaclarke

shell/platform/darwin/ios/framework/Source/SemanticsObjectTest.mm

@@ -38,4 +38,30 @@ - (void)testCreate {
   XCTAssertNotNil(object);
 }
 
+- (void)testSetChildren {
+  fml::WeakPtrFactory<flutter::AccessibilityBridgeIos> factory(
+      new flutter::MockAccessibilityBridge());
+  fml::WeakPtr<flutter::AccessibilityBridgeIos> bridge = factory.GetWeakPtr();
+  SemanticsObject* parent = [[SemanticsObject alloc] initWithBridge:bridge uid:0];
+  SemanticsObject* child = [[SemanticsObject alloc] initWithBridge:bridge uid:1];
+  parent.children = @[child];
+  XCTAssertEqual(parent, child.parent, @"");
+  parent.children = @[];
+  XCTAssertNil(child.parent, @"");
+}
+
+- (void)testReplaceChildAtIndex {
+  fml::WeakPtrFactory<flutter::AccessibilityBridgeIos> factory(
+      new flutter::MockAccessibilityBridge());
+  fml::WeakPtr<flutter::AccessibilityBridgeIos> bridge = factory.GetWeakPtr();
+  SemanticsObject* parent = [[SemanticsObject alloc] initWithBridge:bridge uid:0];
+  SemanticsObject* child1 = [[SemanticsObject alloc] initWithBridge:bridge uid:1];
+  SemanticsObject* child2 = [[SemanticsObject alloc] initWithBridge:bridge uid:2];
+  parent.children = @[child1];
+  [parent replaceChildAtIndex:0 withChild:child2];
+  XCTAssertNil(child1.parent, @"");
+  XCTAssertEqual(parent, child2.parent, @"");
+  XCTAssertEqualObjects(parent.children, @[child2], @"");
+}
+
 @end

testing/ios/IosUnitTests/build_and_run_tests.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -e
+
 FLUTTER_ENGINE=ios_debug_sim_unopt
 
 if [ $# -eq 1 ]; then