Migrate dd-trace-core groovy files to java part 4

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"

dd-trace-core/src/test/java/datadog/trace/core/ControllableSampler.java

@@ -0,0 +1,20 @@
+package datadog.trace.core;
+
+import datadog.trace.api.sampling.PrioritySampling;
+import datadog.trace.api.sampling.SamplingMechanism;
+import datadog.trace.common.sampling.PrioritySampler;
+import datadog.trace.common.sampling.Sampler;
+
+public class ControllableSampler implements Sampler, PrioritySampler {
+  protected int nextSamplingPriority = PrioritySampling.SAMPLER_KEEP;
+
+  @Override
+  public <T extends CoreSpan<T>> void setSamplingPriority(T span) {
+    span.setSamplingPriority(nextSamplingPriority, SamplingMechanism.DEFAULT);
+  }
+
+  @Override
+  public <T extends CoreSpan<T>> boolean sample(T span) {
+    return true;
+  }
+}