Improve error reporting in edge cases.

When a failure happens after the test suite has stopped (or started),
the failure message included the description of the class XCTestRun or
XCTestCaseRun, which is the default description.

Since those errors are difficult to trace back, instead of logging an
unhelpful source/line location pointing to the inside of XCTest, log the
additional information passed in into the method, to help the user to
locate their error.

Author: drodriguez

Sources/XCTest/Public/XCTestRun.swift

@@ -119,13 +119,21 @@ open class XCTestRun {
     ///   result of a failed assertion, `false` if it was the result of an
     ///   uncaught exception.
     func recordFailure(withDescription description: String, inFile filePath: String?, atLine lineNumber: Int, expected: Bool) {
+        func failureLocation() -> String {
+            if let filePath = filePath {
+                return "\(test.name) (\(filePath):\(lineNumber))"
+            } else {
+                return "\(test.name)"
+            }
+        }
+
         guard isStarted else {
             fatalError("Invalid attempt to record a failure for a test run " +
-                       "that has not yet been started: \(self)")
+                       "that has not yet been started: \(failureLocation())")
         }
         guard !isStopped else {
             fatalError("Invalid attempt to record a failure for a test run " +
-                       "that has already been stopped: \(self)")
+                       "that has already been stopped: \(failureLocation())")
         }
 
         if expected {