Promote Error to LocalizedError

Sources/t/t.swift

@@ -1,10 +1,16 @@
+import Foundation
+
 /// A simple way to test expectations using functions and errors
 public enum t {
     /// Simple Error with a description stating the failure
-    public struct TestError: Error {
+    public struct TestError: LocalizedError {
         public let description: String
         public let lineNumber: Int
         public let functionName: String
         public let fileName: String
+
+        public var errorDescription: String? {
+            "\(description) (file: \(fileName) func: \(functionName)@\(lineNumber))"
+        }
     }
 }