Add bool to manage whether a tracer has been registered in GlobalTrac…

…er (#114)

* add isRegistered internal bool to GlobalTracer

- add s_isRegistered bool
- set s_isregistered when Registering a tracer
- add unit test to verify registering a NoopTracer set the s_isRegistered bool

- move ResetTracer logic to GlobalTracer as internal function instead of test utility for easier reusability

* re-add GlobalTracerTestUtil and use that to reset isRegistered bool

src/OpenTracing/Util/GlobalTracer.cs

@@ -29,6 +29,8 @@ public sealed class GlobalTracer : ITracer
     {
         private static readonly object s_lock = new object();
 
+        private static bool s_isRegistered;
+
         /// <summary>
         /// Singleton instance.
         /// <para/>
@@ -59,7 +61,7 @@ public sealed class GlobalTracer : ITracer
         /// <returns>Whether a tracer has been registered.</returns>
         public static bool IsRegistered()
         {
-            return !(s_instance._tracer is NoopTracer);
+            return s_isRegistered;
         }
 
         /// <summary>
@@ -82,12 +84,16 @@ public static void Register(ITracer tracer)
             lock (s_lock)
             {
                 if (tracer == s_instance._tracer)
+                {
+                    s_isRegistered = true;
                     return;
+                }
 
                 if (IsRegistered())
                     throw new InvalidOperationException("There is already a current global Tracer registered.");
 
                 s_instance._tracer = tracer;
+                s_isRegistered = true;
             }
         }
 

test/OpenTracing.Tests/Util/GlobalTracerTestUtil.cs

@@ -7,6 +7,7 @@ namespace OpenTracing.Tests.Util
     public static class GlobalTracerTestUtil
     {
         private static FieldInfo s_tracerField = typeof(GlobalTracer).GetField("_tracer", BindingFlags.NonPublic | BindingFlags.Instance);
+        private static FieldInfo s_isRegisteredField = typeof(GlobalTracer).GetField("s_isRegistered", BindingFlags.NonPublic | BindingFlags.Static);
 
         /// <summary>
         /// Resets the <see cref="GlobalTracer"/> to its initial, unregistered state.
@@ -24,6 +25,7 @@ public static void SetGlobalTracerUnconditionally(ITracer tracer)
         {
             GlobalTracer globalTracer = (GlobalTracer)GlobalTracer.Instance;
             s_tracerField.SetValue(globalTracer, tracer);
+            s_isRegisteredField.SetValue(globalTracer, false);
         }
     }
 }

test/OpenTracing.Tests/Util/GlobalTracerTests.cs

@@ -61,6 +61,14 @@ public void Registering_null_fails()
             Assert.Throws<ArgumentNullException>(() => GlobalTracer.Register(null));
         }
 
+        [Fact]
+        public void Registering_NoopTracer_indicates_tracer_has_been_registered()
+        {
+            Assert.False(GlobalTracer.IsRegistered());
+            GlobalTracer.Register(NoopTracerFactory.Create());
+            Assert.True(GlobalTracer.IsRegistered());
+        }
+
         [Fact]
         public void NoopTracer_is_set_by_default()
         {