Migrate dd-trace-core groovy files to java part 2

migrate DDSpecification and DDCoreSpecification that are used by most
of the test in this module.
we are keeping the groovy version to be able to incrementally migrate
tests.
a first small test (DDSpanLinkTest )is migrated to prove the viability
of the strategy.

Author: jpbempel

dd-trace-core/src/test/groovy/datadog/trace/core/DDSpanLinkTest.groovy

@@ -0,0 +1,138 @@
+package datadog.trace.core;
+
+import datadog.metrics.api.statsd.StatsDClient;
+import datadog.trace.api.DDSpanId;
+import datadog.trace.api.DDTraceId;
+import datadog.trace.api.datastreams.NoopPathwayContext;
+import datadog.trace.api.sampling.PrioritySampling;
+import datadog.trace.bootstrap.instrumentation.api.Baggage;
+import datadog.trace.bootstrap.instrumentation.api.ProfilingContextIntegration;
+import datadog.trace.common.writer.ListWriter;
+import datadog.trace.core.CoreTracer.CoreTracerBuilder;
+import datadog.trace.core.propagation.PropagationTags;
+import datadog.trace.core.tagprocessor.TagsPostProcessorFactory;
+import datadog.trace.test.util.DDJavaSpecification;
+import datadog.trace.util.AgentTaskScheduler;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeAll;
+
+public abstract class DDCoreJavaSpecification extends DDJavaSpecification {
+
+  protected static List<CoreTracer> unclosedTracers = new ArrayList<>();
+
+  protected static class AutoCloseableCoreTracerBuilder extends CoreTracerBuilder {
+    @Override
+    public CoreTracer build() {
+      CoreTracer tracer = super.build();
+      unclosedTracers.add(tracer);
+      return tracer;
+    }
+  }
+
+  protected boolean useNoopStatsDClient() {
+    return true;
+  }
+
+  protected boolean useStrictTraceWrites() {
+    return true;
+  }
+
+  @BeforeAll
+  void setupCoreSpec() {
+    TagsPostProcessorFactory.withAddInternalTags(false);
+    TagsPostProcessorFactory.withAddRemoteHostname(false);
+  }
+
+  @AfterAll
+  void cleanupCoreSpec() {
+    TagsPostProcessorFactory.reset();
+  }
+
+  @AfterEach
+  void cleanupCore() throws Exception {
+    for (CoreTracer tracer : unclosedTracers) {
+      try {
+        tracer.close();
+      } catch (Throwable ignored) {
+      }
+    }
+    unclosedTracers.clear();
+    AgentTaskScheduler.shutdownAndReset(10, TimeUnit.SECONDS);
+  }
+
+  protected CoreTracerBuilder tracerBuilder() {
+    CoreTracerBuilder builder = new AutoCloseableCoreTracerBuilder();
+    if (useNoopStatsDClient()) {
+      builder = builder.statsDClient(StatsDClient.NO_OP);
+    }
+    return builder.strictTraceWrites(useStrictTraceWrites());
+  }
+
+  protected DDSpan buildSpan(long timestamp, CharSequence spanType, Map<String, Object> tags) {
+    return buildSpan(
+        timestamp,
+        spanType,
+        PropagationTags.factory().empty(),
+        tags,
+        PrioritySampling.SAMPLER_KEEP,
+        null);
+  }
+
+  protected DDSpan buildSpan(
+      long timestamp, String tag, String value, PropagationTags propagationTags) {
+    Map<String, Object> tags = new HashMap<>();
+    tags.put(tag, value);
+    return buildSpan(timestamp, "fakeType", propagationTags, tags, PrioritySampling.UNSET, null);
+  }
+
+  protected DDSpan buildSpan(
+      long timestamp,
+      CharSequence spanType,
+      PropagationTags propagationTags,
+      Map<String, Object> tags,
+      byte prioritySampling,
+      Object ciVisibilityContextData) {
+    CoreTracer tracer = tracerBuilder().writer(new ListWriter()).build();
+    DDSpanContext context =
+        new DDSpanContext(
+            DDTraceId.ONE,
+            1L,
+            DDSpanId.ZERO,
+            null,
+            null,
+            "fakeService",
+            "fakeOperation",
+            "fakeResource",
+            prioritySampling,
+            null,
+            Collections.emptyMap(),
+            (Baggage) null,
+            false,
+            spanType,
+            0,
+            tracer.createTraceCollector(DDTraceId.ONE),
+            null,
+            null,
+            ciVisibilityContextData,
+            NoopPathwayContext.INSTANCE,
+            false,
+            propagationTags,
+            ProfilingContextIntegration.NoOp.INSTANCE,
+            true);
+
+    DDSpan span = DDSpan.create("test", timestamp, context, null);
+    for (Map.Entry<String, Object> entry : tags.entrySet()) {
+      span.setTag(entry.getKey(), entry.getValue());
+    }
+
+    tracer.close();
+    return span;
+  }
+}