Allow ScopeManager.active().close() and let it be a no-op

src/main/java/brave/opentracing/BraveScopeManager.java

@@ -38,15 +38,14 @@ public final class BraveScopeManager implements ScopeManager {
   /**
    * This api's only purpose is to retrieve the {@link Scope#span() span}.
    *
-   * @throws IllegalStateException if you attempt to close the resulting scope.
+   * Calling {@link Scope#close() close } on the returned scope has no effect on the active span
    */
   @Override public Scope active() {
     BraveSpan span = currentSpan();
     if (span == null) return null;
     return new Scope() {
       @Override public void close() {
-        throw new IllegalStateException(
-            "Scope should not be closed via ScopeManager.active().close()");
+        // no-op
       }
 
       @Override public Span span() {

src/test/java/brave/opentracing/BraveScopeManagerTest.java

@@ -23,7 +23,6 @@
 import org.junit.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.failBecauseExceptionWasNotThrown;
 
 public class BraveScopeManagerTest {
 
@@ -74,15 +73,12 @@ public class BraveScopeManagerTest {
     }
   }
 
-  @Test public void scopeManagerActiveClose_unsupported() {
-    BraveSpan span = opentracing.buildSpan("spanA").start();
-    try (Scope scopeA = opentracing.scopeManager().activate(span, false)) {
+  @Test public void scopeManagerActiveClose() {
+    BraveSpan spanA = opentracing.buildSpan("spanA").start();
+    try (Scope scopeA = opentracing.scopeManager().activate(spanA, false)) {
       Scope scopeB = opentracing.scopeManager().active();
-      try {
-        scopeB.close();
-        failBecauseExceptionWasNotThrown(IllegalStateException.class);
-      } catch (IllegalStateException e) {
-      }
+
+      scopeB.close();
     }
   }