diff --git a/opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java b/opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java
index 042d20ad..f4225484 100644
--- a/opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java
+++ b/opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java
@@ -13,23 +13,23 @@
  */
 package io.opentracing.mock;
 
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
 import io.opentracing.ActiveSpan;
 import io.opentracing.ActiveSpanSource;
 import io.opentracing.BaseSpan;
-import io.opentracing.noop.NoopActiveSpanSource;
 import io.opentracing.References;
 import io.opentracing.Span;
 import io.opentracing.SpanContext;
 import io.opentracing.Tracer;
+import io.opentracing.noop.NoopActiveSpanSource;
 import io.opentracing.propagation.Format;
 import io.opentracing.propagation.TextMap;
 import io.opentracing.util.ThreadLocalActiveSpanSource;
 
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-
 /**
  * MockTracer makes it easy to test the semantics of OpenTracing instrumentation.
  *
@@ -39,16 +39,16 @@
  * The MockTracerTest has simple usage examples.
  */
 public class MockTracer implements Tracer {
-    private List<MockSpan> finishedSpans = new ArrayList<>();
+    private final List<MockSpan> finishedSpans = new ArrayList<>();
     private final Propagator propagator;
-    private ActiveSpanSource spanSource;
+    private final ActiveSpanSource spanSource;
 
     public MockTracer() {
-        this(new ThreadLocalActiveSpanSource(), Propagator.PRINTER);
+        this(new ThreadLocalActiveSpanSource(), Propagator.TEXT_MAP);
     }
 
     public MockTracer(ActiveSpanSource spanSource) {
-        this(spanSource, Propagator.PRINTER);
+        this(spanSource, Propagator.TEXT_MAP);
     }
 
     public MockTracer(ActiveSpanSource spanSource, Propagator propagator) {
diff --git a/opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java b/opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java
index 2f2a410b..a9243cb5 100644
--- a/opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java
+++ b/opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java
@@ -14,20 +14,24 @@
 package io.opentracing.mock;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
 
 import io.opentracing.References;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import io.opentracing.ActiveSpan;
 import io.opentracing.Span;
 import io.opentracing.SpanContext;
 import io.opentracing.Tracer;
 import io.opentracing.propagation.Format;
 import io.opentracing.propagation.TextMapExtractAdapter;
 import io.opentracing.propagation.TextMapInjectAdapter;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-import org.junit.Assert;
-import org.junit.Test;
 
 public class MockTracerTest {
     @Test
@@ -277,6 +281,18 @@ public void testNonStandardReference() {
 
         assertEquals(parent.context().spanId(), nextSpan.parentId());
         assertEquals(1, nextSpan.references().size());
-        assertEquals(nextSpan.references().get(0), new MockSpan.Reference(parent.context(), "a_reference"));
+        assertEquals(nextSpan.references().get(0),
+            new MockSpan.Reference(parent.context(), "a_reference"));
+    }
+
+    @Test
+    public void testDefaultConstructor() {
+        MockTracer mockTracer = new MockTracer();
+        ActiveSpan activeSpan = mockTracer.buildSpan("foo").startActive();
+        assertEquals(activeSpan, mockTracer.activeSpan());
+
+        Map<String, String> propag = new HashMap<>();
+        mockTracer.inject(activeSpan.context(), Format.Builtin.TEXT_MAP, new TextMapInjectAdapter(propag));
+        assertFalse(propag.isEmpty());
     }
 }