adding tests

dd-java-agent/dd-java-agent.gradle

@@ -55,6 +55,7 @@ dependencies {
     exclude(group: 'org.apache.httpcomponents', module: 'httpclient')
   }
 
+  testCompile group: 'org.mongodb', name: 'mongo-java-driver', version: '3.4.2'
   testCompile group: 'io.opentracing', name: 'opentracing-mock', version: '0.30.0'
   testCompile group: 'junit', name: 'junit', version: '4.12'
   testCompile group: 'org.assertj', name: 'assertj-core', version: '3.6.2'

dd-java-agent/src/test/java/com/datadoghq/trace/agent/integration/MongoHelperTest.java

@@ -0,0 +1,26 @@
+package com.datadoghq.trace.agent.integration;
+
+import static org.assertj.core.api.Java6Assertions.assertThat;
+
+import com.datadoghq.trace.DDSpan;
+import com.datadoghq.trace.DDTracer;
+import com.mongodb.event.CommandStartedEvent;
+import org.bson.BsonDocument;
+import org.junit.Test;
+
+public class MongoHelperTest {
+
+  @Test
+  public void test() {
+
+    final CommandStartedEvent cmd =
+        new CommandStartedEvent(1, null, "databasename", "query", new BsonDocument());
+
+    final DDSpan span = new DDTracer().buildSpan("foo").startManual();
+    new MongoHelper(null).decorate(span, cmd);
+
+    assertThat(span.context().getSpanType()).isEqualTo("mongodb");
+    assertThat(span.context().getResourceName())
+        .isEqualTo(span.context().getTags().get("db.statement"));
+  }
+}