fix ServiceNameCollector singleton

we save the original instance before replaced by mock to restore it
Some tests rely on having. the original, and depending on the order
the class my keep the mocks instead resulting in errors

Author: jpbempel

dd-trace-core/src/test/groovy/datadog/trace/core/taginterceptor/TagInterceptorTest.groovy

@@ -696,6 +696,7 @@ class TagInterceptorTest extends DDCoreSpecification {
   }
 
   void "when interceptServiceName extraServiceProvider is called"() {
+    def origServiceNameCollector = ServiceNameCollector.INSTANCE
     setup:
     final extraServiceProvider = Mock(ServiceNameCollector)
     ServiceNameCollector.INSTANCE = extraServiceProvider
@@ -708,9 +709,13 @@ class TagInterceptorTest extends DDCoreSpecification {
 
     then:
     1 * extraServiceProvider.addService("some-service")
+
+    cleanup:
+    ServiceNameCollector.INSTANCE = origServiceNameCollector
   }
 
   void "when interceptServletContext extraServiceProvider is called"() {
+    def origServiceNameCollector = ServiceNameCollector.INSTANCE
     setup:
     final extraServiceProvider = Mock(ServiceNameCollector)
     ServiceNameCollector.INSTANCE = extraServiceProvider
@@ -724,6 +729,9 @@ class TagInterceptorTest extends DDCoreSpecification {
     then:
     1 * extraServiceProvider.addService(expected)
 
+    cleanup:
+    ServiceNameCollector.INSTANCE = origServiceNameCollector
+
     where:
     value   | expected
     "/"     | "root-servlet"

internal-api/src/test/groovy/datadog/trace/api/naming/ExtraServiceProviderNamingV0ForkedTest.groovy

@@ -7,6 +7,7 @@ import datadog.trace.api.remoteconfig.ServiceNameCollector
 class ExtraServiceProviderNamingV0ForkedTest extends DDSpecification {
 
   void "Naming schema calls ExtraServicesProvider if provides a service name"() {
+    def origServiceNameCollector = ServiceNameCollector.INSTANCE
     setup:
     final extraServiceProvider = Mock(ServiceNameCollector)
     ServiceNameCollector.INSTANCE = extraServiceProvider
@@ -67,5 +68,8 @@ class ExtraServiceProviderNamingV0ForkedTest extends DDSpecification {
 
     then:
     1 * extraServiceProvider.addService("anything")
+
+    cleanup:
+    ServiceNameCollector.INSTANCE = origServiceNameCollector
   }
 }