tests: Use demangled value in assertion

Mangled swift is unstable and differs a lot between versions

features/handled_errors.feature

@@ -12,7 +12,7 @@ Scenario: Override errorClass and message from a notifyError() callback and disc
     And the exception "errorClass" equals "Bar"
     And the exception "message" equals "Foo"
     And the event "device.time" is within 30 seconds of the current timestamp
-    And the "method" of stack frame 0 equals "$S10iOSTestApp28HandledErrorOverrideScenarioC3runyyF"
+    And the "method" of stack frame 0 demangles to "iOSTestApp.HandledErrorOverrideScenario.run() -> ()"
     And the stack trace is an array with 15 stack frames
 
 Scenario: Reporting an NSError

features/steps/ios_steps.rb

@@ -120,6 +120,12 @@
   assert_not_nil(match, "No crumb matches the provided message")
 end
 
+Then("the {string} of stack frame {int} demangles to {string}") do |field, frame_index, expected_value|
+  value = read_key_path(find_request(0)[:body], "events.0.exceptions.0.stacktrace.#{frame_index}.#{field}")
+  demangled_value = `xcrun swift-demangle -compact '#{value}'`.chomp
+  assert_equal(expected_value, demangled_value)
+end
+
 Then("the stack trace is an array with {int} stack frames") do |expected_length|
   stack_trace = read_key_path(find_request(0)[:body], "events.0.exceptions.0.stacktrace")
   assert_equal(expected_length,  stack_trace.length)