Cleanup trace API (#121)

* Cleanups:
Use directly the static final variable for INVALID and DEFAULT.
Add a SpanId class.
deps for trace in BUILD. 
Fix samplers to use the new SpanId.

18 files changed, 229 insertions, 95 deletions

diff --git a/core/src/main/java/com/google/instrumentation/trace/BlankSpan.java b/core/src/main/java/com/google/instrumentation/trace/BlankSpan.java
index bbe31df2..a77b4af0 100644
--- a/core/src/main/java/com/google/instrumentation/trace/BlankSpan.java
+++ b/core/src/main/java/com/google/instrumentation/trace/BlankSpan.java
@@ -29,7 +29,7 @@ public final class BlankSpan extends Span {
   public static final BlankSpan INSTANCE = new BlankSpan();
 
   private BlankSpan() {
-    super(SpanContext.getInvalid(), null);
+    super(SpanContext.INVALID, null);
   }
 
   /**
diff --git a/core/src/main/java/com/google/instrumentation/trace/EndSpanOptions.java b/core/src/main/java/com/google/instrumentation/trace/EndSpanOptions.java
index b7abfaa6..2b74d0ca 100644
--- a/core/src/main/java/com/google/instrumentation/trace/EndSpanOptions.java
+++ b/core/src/main/java/com/google/instrumentation/trace/EndSpanOptions.java
@@ -28,27 +28,20 @@ import javax.annotation.concurrent.Immutable;
  */
 @Immutable
 public final class EndSpanOptions {
-  // Default set of options.
-  private static final EndSpanOptions DEFAULT_OPTIONS = builder().build();
-
   private final Status status;
   private final Timestamp endTime;
 
+  /**
+   * The default {@code EndSpanOptions}.
+   */
+  public static final EndSpanOptions DEFAULT = builder().build();
+
   private EndSpanOptions(Timestamp endTime, Status status) {
     this.endTime = endTime;
     this.status = status;
   }
 
   /**
-   * Returns default {@code EndSpanOptions}.
-   *
-   * @return default {@code EndSpanOptions}.
-   */
-  public static EndSpanOptions getDefault() {
-    return DEFAULT_OPTIONS;
-  }
-
-  /**
    * Returns a new {@link Builder} with default options.
    *
    * @return a new {@code Builder} with default options.
diff --git a/core/src/main/java/com/google/instrumentation/trace/Sampler.java b/core/src/main/java/com/google/instrumentation/trace/Sampler.java
index c1d5b303..bf294a5c 100644
--- a/core/src/main/java/com/google/instrumentation/trace/Sampler.java
+++ b/core/src/main/java/com/google/instrumentation/trace/Sampler.java
@@ -37,7 +37,7 @@ public abstract class Sampler {
       @Nullable SpanContext parentContext,
       boolean remoteParent,
       TraceId traceId,
-      long spanId,
+      SpanId spanId,
       String name,
       List<Span> parentLinks);
 }
diff --git a/core/src/main/java/com/google/instrumentation/trace/Samplers.java b/core/src/main/java/com/google/instrumentation/trace/Samplers.java
index 59983b2d..0c7ef3cd 100644
--- a/core/src/main/java/com/google/instrumentation/trace/Samplers.java
+++ b/core/src/main/java/com/google/instrumentation/trace/Samplers.java
@@ -53,7 +53,7 @@ public final class Samplers {
         @Nullable SpanContext parentContext,
         boolean remoteParent,
         TraceId traceId,
-        long spanId,
+        SpanId spanId,
         String name,
         List<Span> parentLinks) {
       return true;
@@ -74,7 +74,7 @@ public final class Samplers {
         @Nullable SpanContext parentContext,
         boolean remoteParent,
         TraceId traceId,
-        long spanId,
+        SpanId spanId,
         String name,
         List<Span> parentLinks) {
       return false;
diff --git a/core/src/main/java/com/google/instrumentation/trace/ScopedSpanHandle.java b/core/src/main/java/com/google/instrumentation/trace/ScopedSpanHandle.java
index 5c24d1fa..1ac67a45 100644
--- a/core/src/main/java/com/google/instrumentation/trace/ScopedSpanHandle.java
+++ b/core/src/main/java/com/google/instrumentation/trace/ScopedSpanHandle.java
@@ -44,6 +44,6 @@ final class ScopedSpanHandle implements NonThrowingCloseable {
   @Override
   public void close() {
     withSpan.close();
-    span.end(EndSpanOptions.getDefault());
+    span.end(EndSpanOptions.DEFAULT);
   }
 }
diff --git a/core/src/main/java/com/google/instrumentation/trace/Span.java b/core/src/main/java/com/google/instrumentation/trace/Span.java
index b883cf62..26de28f7 100644
--- a/core/src/main/java/com/google/instrumentation/trace/Span.java
+++ b/core/src/main/java/com/google/instrumentation/trace/Span.java
@@ -122,7 +122,7 @@ public abstract class Span implements NonThrowingCloseable {
    * implementations are free to ignore all further calls.
    */
   public final void end() {
-    end(EndSpanOptions.getDefault());
+    end(EndSpanOptions.DEFAULT);
   }
 
   /**
@@ -148,6 +148,6 @@ public abstract class Span implements NonThrowingCloseable {
    */
   @Override
   public final void close() {
-    end(EndSpanOptions.getDefault());
+    end(EndSpanOptions.DEFAULT);
   }
 }
diff --git a/core/src/main/java/com/google/instrumentation/trace/SpanContext.java b/core/src/main/java/com/google/instrumentation/trace/SpanContext.java
index fba02939..916ad030 100644
--- a/core/src/main/java/com/google/instrumentation/trace/SpanContext.java
+++ b/core/src/main/java/com/google/instrumentation/trace/SpanContext.java
@@ -16,35 +16,34 @@ package com.google.instrumentation.trace;
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Objects;
 
-import java.util.Formatter;
-import java.util.Locale;
 import javax.annotation.concurrent.Immutable;
 
 /**
  * A class that represents a span context. A span context contains the state that must propagate
  * to child {@link Span}s and across process boundaries. It contains the identifiers (a {@link
- * TraceId trace_id} and span_id) associated with the {@link Span} and a set of {@link TraceOptions
- * options}.
+ * TraceId trace_id} and {@link SpanId span_id}) associated with the {@link Span} and a set of
+ * {@link TraceOptions options}.
  */
 @Immutable
 public final class SpanContext {
-  private static final long INVALID_SPAN_ID = 0;
-
-  private static final SpanContext INVALID_CONTEXT =
-      new SpanContext(TraceId.getInvalid(), INVALID_SPAN_ID, TraceOptions.getDefault());
-
   private final TraceId traceId;
-  private final long spanId;
+  private final SpanId spanId;
   private final TraceOptions traceOptions;
 
   /**
+   * The invalid {@code SpanContext}.
+   */
+  public static final SpanContext INVALID =
+      new SpanContext(TraceId.INVALID, SpanId.INVALID, TraceOptions.getDefault());
+
+  /**
    * Creates a new {@code SpanContext} with the given identifiers and options.
    *
    * @param traceId the trace identifier of the span context.
    * @param spanId the span identifier of the span context.
    * @param traceOptions the trace options for the span context.
    */
-  SpanContext(TraceId traceId, long spanId, TraceOptions traceOptions) {
+  SpanContext(TraceId traceId, SpanId spanId, TraceOptions traceOptions) {
     this.traceId = traceId;
     this.spanId = spanId;
     this.traceOptions = traceOptions;
@@ -64,7 +63,7 @@ public final class SpanContext {
    *
    * @return the span identifier associated with this {@code SpanContext}.
    */
-  public long getSpanId() {
+  public SpanId getSpanId() {
     return spanId;
   }
 
@@ -83,16 +82,7 @@ public final class SpanContext {
    * @return true if this {@code SpanContext} is valid.
    */
   public boolean isValid() {
-    return traceId.isValid() && spanId != INVALID_SPAN_ID;
-  }
-
-  /**
-   * Returns an invalid {@code SpanContext}.
-   *
-   * @return an invalid {@code SpanContext}.
-   */
-  public static SpanContext getInvalid() {
-    return INVALID_CONTEXT;
+    return traceId.isValid() && spanId.isValid();
   }
 
   @Override
@@ -107,7 +97,7 @@ public final class SpanContext {
 
     SpanContext that = (SpanContext) obj;
     return traceId.equals(that.traceId)
-        && spanId == that.spanId
+        && spanId.equals(that.spanId)
         && traceOptions.equals(that.traceOptions);
   }
 
@@ -120,7 +110,7 @@ public final class SpanContext {
   public String toString() {
     return MoreObjects.toStringHelper(this)
         .add("traceId", traceId)
-        .add("spanId", new Formatter(Locale.US).format("%016x", spanId).toString())
+        .add("spanId", spanId)
         .add("traceOptions", traceOptions)
         .toString();
   }
diff --git a/core/src/main/java/com/google/instrumentation/trace/SpanId.java b/core/src/main/java/com/google/instrumentation/trace/SpanId.java
new file mode 100644
index 00000000..302aea35
--- /dev/null
+++ b/core/src/main/java/com/google/instrumentation/trace/SpanId.java
@@ -0,0 +1,87 @@
+/*
+ * Copyright 2017, Google Inc.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.instrumentation.trace;
+
+import com.google.common.base.MoreObjects;
+import com.google.common.base.Objects;
+
+import java.util.Formatter;
+import java.util.Locale;
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * A class that represents a span identifier. A span identifier is a 64-bit, unsigned integer.
+ */
+@Immutable
+public final class SpanId {
+  private static final long INVALID_SPAN_ID = 0;
+  private final long spanId;
+
+  /**
+   * The invalid {@code SpanId}.
+   */
+  public static final SpanId INVALID = new SpanId(INVALID_SPAN_ID);
+
+  /**
+   * Creates a span identifier whose value is taken from the given {@code long}.
+   *
+   * @param spanId a long used as the span identifier.
+   */
+  SpanId(long spanId) {
+    this.spanId = spanId;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (obj == this) {
+      return true;
+    }
+
+    if (!(obj instanceof SpanId)) {
+      return false;
+    }
+
+    SpanId that = (SpanId)obj;
+    return spanId == that.spanId;
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hashCode(spanId);
+  }
+
+  @Override
+  public String toString() {
+    return MoreObjects.toStringHelper(this)
+        .add("spanId", new Formatter(Locale.US).format("%016x", spanId))
+        .toString();
+  }
+  /**
+   * Returns whether the span identifier is valid. A valid span identifer is non-zero long value.
+   *
+   * @return whether the span identifier is valid.
+   */
+  public boolean isValid() {
+    return spanId != INVALID_SPAN_ID;
+  }
+
+  /**
+   * Returns the long that represents the span identifier.
+   *
+   * @return the span identifier.
+   */
+  public long getSpanId() {
+    return spanId;
+  }
+}
diff --git a/core/src/main/java/com/google/instrumentation/trace/TraceId.java b/core/src/main/java/com/google/instrumentation/trace/TraceId.java
index 551e0d17..46492dbd 100644
--- a/core/src/main/java/com/google/instrumentation/trace/TraceId.java
+++ b/core/src/main/java/com/google/instrumentation/trace/TraceId.java
@@ -26,11 +26,15 @@ import javax.annotation.concurrent.Immutable;
  */
 @Immutable
 public final class TraceId {
-  private static final TraceId INVALID_ID = new TraceId(0, 0);
   private final long traceIdHi;
   private final long traceIdLo;
 
   /**
+   * The invalid {@code TraceId}.
+   */
+  public static final TraceId INVALID = new TraceId(0, 0);
+
+  /**
    * Creates a new {@code TraceId} whose value is taken from the given params.
    *
    * @param traceIdHi the higher bits.
@@ -65,16 +69,7 @@ public final class TraceId {
    * @return true if the {@code TraceId} is valid.
    */
   public boolean isValid() {
-    return !this.equals(INVALID_ID);
-  }
-
-  /**
-   * Returns the invalid {@code TraceId}.
-   *
-   * @return the invalid {@code TraceId}.
-   */
-  public static TraceId getInvalid() {
-    return INVALID_ID;
+    return traceIdLo != 0 || traceIdHi != 0;
   }
 
   @Override
diff --git a/core/src/test/java/com/google/instrumentation/trace/BlankSpanTest.java b/core/src/test/java/com/google/instrumentation/trace/BlankSpanTest.java
index 72d48f7e..b6fb865f 100644
--- a/core/src/test/java/com/google/instrumentation/trace/BlankSpanTest.java
+++ b/core/src/test/java/com/google/instrumentation/trace/BlankSpanTest.java
@@ -24,7 +24,7 @@ import org.junit.runners.JUnit4;
 public class BlankSpanTest {
   @Test
   public void hasInvalidContextAndDefaultSpanOptions() {
-    assertThat(BlankSpan.INSTANCE.getContext()).isEqualTo(SpanContext.getInvalid());
+    assertThat(BlankSpan.INSTANCE.getContext()).isEqualTo(SpanContext.INVALID);
     assertThat(BlankSpan.INSTANCE.getOptions().isEmpty()).isTrue();
   }
 
@@ -40,7 +40,7 @@ public class BlankSpanTest {
     BlankSpan.INSTANCE
         .addNetworkEvent(NetworkEvent.builder(NetworkEvent.Type.SENT, 1L).build());
     BlankSpan.INSTANCE.addChildLink(BlankSpan.INSTANCE);
-    BlankSpan.INSTANCE.end(EndSpanOptions.getDefault());
+    BlankSpan.INSTANCE.end(EndSpanOptions.DEFAULT);
   }
 
   @Test
diff --git a/core/src/test/java/com/google/instrumentation/trace/EndSpanOptionsTest.java b/core/src/test/java/com/google/instrumentation/trace/EndSpanOptionsTest.java
index 67aa36ac..a2fb4f63 100644
--- a/core/src/test/java/com/google/instrumentation/trace/EndSpanOptionsTest.java
+++ b/core/src/test/java/com/google/instrumentation/trace/EndSpanOptionsTest.java
@@ -31,8 +31,8 @@ public class EndSpanOptionsTest {
 
   @Test
   public void endSpanOptions_DefaultOptions() {
-    assertThat(EndSpanOptions.getDefault().getStatus()).isEqualTo(Status.OK);
-    assertThat(EndSpanOptions.getDefault().getEndTime()).isNull();
+    assertThat(EndSpanOptions.DEFAULT.getStatus()).isEqualTo(Status.OK);
+    assertThat(EndSpanOptions.DEFAULT.getEndTime()).isNull();
   }
 
   @Test
@@ -70,7 +70,7 @@ public class EndSpanOptionsTest {
             .setEndTime(Timestamp.fromMillis(123456L))
             .setStatus(Status.CANCELLED.withDescription("ThisIsAnError"))
             .build());
-    tester.addEqualityGroup(EndSpanOptions.builder().build(), EndSpanOptions.getDefault());
+    tester.addEqualityGroup(EndSpanOptions.builder().build(), EndSpanOptions.DEFAULT);
     tester.testEquals();
   }
 
diff --git a/core/src/test/java/com/google/instrumentation/trace/SamplersTest.java b/core/src/test/java/com/google/instrumentation/trace/SamplersTest.java
index ece59813..8266bcb2 100644
--- a/core/src/test/java/com/google/instrumentation/trace/SamplersTest.java
+++ b/core/src/test/java/com/google/instrumentation/trace/SamplersTest.java
@@ -26,14 +26,16 @@ public class SamplersTest {
   @Test
   public void alwaysSampleSampler_AlwaysReturnTrue() {
     TraceId traceId = new TraceId(2, 3);
+    SpanId parentSpanId = new SpanId(17);
+    SpanId spanId = new SpanId(42);
     // Traced parent.
     assertThat(
             Samplers.alwaysSample()
                 .shouldSample(
-                    new SpanContext(traceId, 17, new TraceOptions(TraceOptions.IS_SAMPLED)),
+                    new SpanContext(traceId, parentSpanId, new TraceOptions(TraceOptions.IS_SAMPLED)),
                     false,
                     traceId,
-                    42,
+                    spanId,
                     "Another name",
                     Collections.emptyList()))
         .isTrue();
@@ -41,10 +43,10 @@ public class SamplersTest {
     assertThat(
             Samplers.alwaysSample()
                 .shouldSample(
-                    new SpanContext(traceId, 19, new TraceOptions(0)),
+                    new SpanContext(traceId, parentSpanId, new TraceOptions(0)),
                     false,
                     traceId,
-                    42,
+                    spanId,
                     "Yet another name",
                     Collections.emptyList()))
         .isTrue();
@@ -58,14 +60,16 @@ public class SamplersTest {
   @Test
   public void neverSampleSampler_AlwaysReturnFalse() {
     TraceId traceId = new TraceId(4, 5);
+    SpanId parentSpanId = new SpanId(19);
+    SpanId spanId = new SpanId(42);
     // Traced parent.
     assertThat(
             Samplers.neverSample()
                 .shouldSample(
-                    new SpanContext(traceId, 17, new TraceOptions(TraceOptions.IS_SAMPLED)),
+                    new SpanContext(traceId, parentSpanId, new TraceOptions(TraceOptions.IS_SAMPLED)),
                     false,
                     traceId,
-                    42,
+                    spanId,
                     "bar",
                     Collections.emptyList()))
         .isFalse();
@@ -73,10 +77,10 @@ public class SamplersTest {
     assertThat(
             Samplers.neverSample()
                 .shouldSample(
-                    new SpanContext(traceId, 17, new TraceOptions(0)),
+                    new SpanContext(traceId, parentSpanId, new TraceOptions(0)),
                     false,
                     traceId,
-                    42,
+                    spanId,
                     "quux",
                     Collections.emptyList()))
         .isFalse();
diff --git a/core/src/test/java/com/google/instrumentation/trace/ScopedSpanHandleTest.java b/core/src/test/java/com/google/instrumentation/trace/ScopedSpanHandleTest.java
index cca32519..971904b1 100644
--- a/core/src/test/java/com/google/instrumentation/trace/ScopedSpanHandleTest.java
+++ b/core/src/test/java/com/google/instrumentation/trace/ScopedSpanHandleTest.java
@@ -46,6 +46,6 @@ public class ScopedSpanHandleTest {
       // Do nothing.
     }
     verify(ntc).close();
-    verify(span).end(same(EndSpanOptions.getDefault()));
+    verify(span).end(same(EndSpanOptions.DEFAULT));
   }
 }
diff --git a/core/src/test/java/com/google/instrumentation/trace/SpanContextTest.java b/core/src/test/java/com/google/instrumentation/trace/SpanContextTest.java
index 30ca1cb4..4cc10bee 100644
--- a/core/src/test/java/com/google/instrumentation/trace/SpanContextTest.java
+++ b/core/src/test/java/com/google/instrumentation/trace/SpanContextTest.java
@@ -24,23 +24,26 @@ import org.junit.runners.JUnit4;
 @RunWith(JUnit4.class)
 public class SpanContextTest {
   private static final SpanContext first =
-      new SpanContext(new TraceId(0, 10), 30, TraceOptions.getDefault());
+      new SpanContext(new TraceId(0, 10), new SpanId(30), TraceOptions.getDefault());
   private static final SpanContext second =
-      new SpanContext(new TraceId(0, 20), 40, new TraceOptions(TraceOptions.IS_SAMPLED));
+      new SpanContext(
+          new TraceId(0, 20), new SpanId(40), new TraceOptions(TraceOptions.IS_SAMPLED));
 
   @Test
   public void invalidSpanContext() {
-    assertThat(SpanContext.getInvalid().getTraceId()).isEqualTo(TraceId.getInvalid());
-    assertThat(SpanContext.getInvalid().getSpanId()).isEqualTo(0);
-    assertThat(SpanContext.getInvalid().getTraceOptions()).isEqualTo(TraceOptions.getDefault());
+    assertThat(SpanContext.INVALID.getTraceId()).isEqualTo(TraceId.INVALID);
+    assertThat(SpanContext.INVALID.getSpanId()).isEqualTo(SpanId.INVALID);
+    assertThat(SpanContext.INVALID.getTraceOptions()).isEqualTo(TraceOptions.getDefault());
   }
 
   @Test
   public void isValid() {
-    assertThat(SpanContext.getInvalid().isValid()).isFalse();
-    assertThat(new SpanContext(new TraceId(0, 10), 0, TraceOptions.getDefault()).isValid())
+    assertThat(SpanContext.INVALID.isValid()).isFalse();
+    assertThat(
+            new SpanContext(new TraceId(0, 10), SpanId.INVALID, TraceOptions.getDefault()).isValid())
         .isFalse();
-    assertThat(new SpanContext(TraceId.getInvalid(), 10, TraceOptions.getDefault()).isValid())
+    assertThat(
+            new SpanContext(TraceId.INVALID, new SpanId(10), TraceOptions.getDefault()).isValid())
         .isFalse();
     assertThat(first.isValid()).isTrue();
     assertThat(second.isValid()).isTrue();
@@ -54,8 +57,8 @@ public class SpanContextTest {
 
   @Test
   public void getSpanId() {
-    assertThat(first.getSpanId()).isEqualTo(30);
-    assertThat(second.getSpanId()).isEqualTo(40);
+    assertThat(first.getSpanId()).isEqualTo(new SpanId(30));
+    assertThat(second.getSpanId()).isEqualTo(new SpanId(40));
   }
 
   @Test
@@ -68,19 +71,21 @@ public class SpanContextTest {
   public void spanContext_EqualsAndHashCode() {
     EqualsTester tester = new EqualsTester();
     tester.addEqualityGroup(
-        first, new SpanContext(new TraceId(0, 10), 30, TraceOptions.getDefault()));
+        first, new SpanContext(new TraceId(0, 10), new SpanId(30), TraceOptions.getDefault()));
     tester.addEqualityGroup(
-        second, new SpanContext(new TraceId(0, 20), 40, new TraceOptions(TraceOptions.IS_SAMPLED)));
+        second,
+        new SpanContext(
+            new TraceId(0, 20), new SpanId(40), new TraceOptions(TraceOptions.IS_SAMPLED)));
     tester.testEquals();
   }
 
   @Test
   public void spanContext_ToString() {
     assertThat(first.toString()).contains(new TraceId(0, 10).toString());
-    assertThat(first.toString()).contains("spanId=000000000000001e");
+    assertThat(first.toString()).contains(new SpanId(30).toString());
     assertThat(first.toString()).contains(TraceOptions.getDefault().toString());
     assertThat(second.toString()).contains(new TraceId(0, 20).toString());
-    assertThat(second.toString()).contains("spanId=0000000000000028");
+    assertThat(second.toString()).contains(new SpanId(40).toString());
     assertThat(second.toString()).contains(new TraceOptions(TraceOptions.IS_SAMPLED).toString());
   }
 }
diff --git a/core/src/test/java/com/google/instrumentation/trace/SpanIdTest.java b/core/src/test/java/com/google/instrumentation/trace/SpanIdTest.java
new file mode 100644
index 00000000..f5c50d25
--- /dev/null
+++ b/core/src/test/java/com/google/instrumentation/trace/SpanIdTest.java
@@ -0,0 +1,59 @@
+/*
+ * Copyright 2017, Google Inc.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.instrumentation.trace;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.testing.EqualsTester;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests for {@link SpanId}. */
+@RunWith(JUnit4.class)
+public class SpanIdTest {
+  private static final SpanId first = new SpanId(123);
+
+  @Test
+  public void invalidSpanId() {
+    assertThat(SpanId.INVALID.getSpanId()).isEqualTo(0);
+  }
+
+  @Test
+  public void isValid() {
+    assertThat(SpanId.INVALID.isValid()).isFalse();
+    assertThat(first.isValid()).isTrue();
+  }
+
+  @Test
+  public void getSpanId() {
+    assertThat(first.getSpanId()).isEqualTo(123);
+  }
+
+  @Test
+  public void traceId_EqualsAndHashCode() {
+    EqualsTester tester = new EqualsTester();
+    tester.addEqualityGroup(SpanId.INVALID, SpanId.INVALID);
+    tester.addEqualityGroup(first, new SpanId(123));
+    tester.testEquals();
+  }
+
+  @Test
+  public void traceId_ToString() {
+    assertThat(SpanId.INVALID.toString()).contains("0000000000000000");
+    assertThat(new SpanId(0xFEDCBA9876543210L).toString())
+        .contains("fedcba9876543210");
+    assertThat(new SpanId(-1).toString()).contains("ffffffffffffffff");
+  }
+}
diff --git a/core/src/test/java/com/google/instrumentation/trace/SpanTest.java b/core/src/test/java/com/google/instrumentation/trace/SpanTest.java
index 0c628253..1864b1a7 100644
--- a/core/src/test/java/com/google/instrumentation/trace/SpanTest.java
+++ b/core/src/test/java/com/google/instrumentation/trace/SpanTest.java
@@ -27,7 +27,7 @@ import org.mockito.Mockito;
 @RunWith(JUnit4.class)
 public class SpanTest {
   private static final SpanContext spanContext =
-      new SpanContext(new TraceId(10, 20), 30, TraceOptions.getDefault());
+      new SpanContext(new TraceId(10, 20), new SpanId(30), TraceOptions.getDefault());
   private static final EnumSet<Span.Options> spanOptions = EnumSet.of(Span.Options.RECORD_EVENTS);
 
   @Test(expected = NullPointerException.class)
@@ -52,14 +52,14 @@ public class SpanTest {
   public void endCallsEndWithDefaultOptions() {
     Span span = Mockito.spy(new NoopSpan(spanContext, spanOptions));
     span.end();
-    verify(span).end(same(EndSpanOptions.getDefault()));
+    verify(span).end(same(EndSpanOptions.DEFAULT));
   }
 
   @Test
   public void closeCallsEndWithDefaultOptions() {
     Span span = Mockito.spy(new NoopSpan(spanContext, spanOptions));
     span.close();
-    verify(span).end(same(EndSpanOptions.getDefault()));
+    verify(span).end(same(EndSpanOptions.DEFAULT));
   }
 
   // No-op implementation of the Span for testing only.
diff --git a/core/src/test/java/com/google/instrumentation/trace/TraceIdTest.java b/core/src/test/java/com/google/instrumentation/trace/TraceIdTest.java
index b611a281..fc9708eb 100644
--- a/core/src/test/java/com/google/instrumentation/trace/TraceIdTest.java
+++ b/core/src/test/java/com/google/instrumentation/trace/TraceIdTest.java
@@ -29,13 +29,13 @@ public class TraceIdTest {
 
   @Test
   public void invalidTraceId() {
-    assertThat(TraceId.getInvalid().getTraceIdLo()).isEqualTo(0);
-    assertThat(TraceId.getInvalid().getTraceIdHi()).isEqualTo(0);
+    assertThat(TraceId.INVALID.getTraceIdLo()).isEqualTo(0);
+    assertThat(TraceId.INVALID.getTraceIdHi()).isEqualTo(0);
   }
 
   @Test
   public void isValid() {
-    assertThat(TraceId.getInvalid().isValid()).isFalse();
+    assertThat(TraceId.INVALID.isValid()).isFalse();
     assertThat(second.isValid()).isTrue();
     assertThat(third.isValid()).isTrue();
     assertThat(first.isValid()).isTrue();
@@ -58,7 +58,7 @@ public class TraceIdTest {
   @Test
   public void traceId_EqualsAndHashCode() {
     EqualsTester tester = new EqualsTester();
-    tester.addEqualityGroup(TraceId.getInvalid(), TraceId.getInvalid());
+    tester.addEqualityGroup(TraceId.INVALID, TraceId.INVALID);
     tester.addEqualityGroup(first, new TraceId(123, 456));
     tester.addEqualityGroup(second, new TraceId(0, 789));
     tester.addEqualityGroup(third, new TraceId(987, 0));
@@ -67,7 +67,7 @@ public class TraceIdTest {
 
   @Test
   public void traceId_ToString() {
-    assertThat(TraceId.getInvalid().toString()).contains("00000000000000000000000000000000");
+    assertThat(TraceId.INVALID.toString()).contains("00000000000000000000000000000000");
     assertThat(new TraceId(0, 0xFEDCBA9876543210L).toString())
         .contains("0000000000000000fedcba9876543210");
     assertThat(new TraceId(0x0123456789ABCDEFL, 0).toString())
diff --git a/core/src/test/java/com/google/instrumentation/trace/TracerTest.java b/core/src/test/java/com/google/instrumentation/trace/TracerTest.java
index c5f07722..de67c6ec 100644
--- a/core/src/test/java/com/google/instrumentation/trace/TracerTest.java
+++ b/core/src/test/java/com/google/instrumentation/trace/TracerTest.java
@@ -229,7 +229,7 @@ public class TracerTest {
     when(contextSpanHandler.withSpan(same(span))).thenReturn(withSpan);
     try (NonThrowingCloseable ss = mockTracer.startScopedSpan("MySpanName")) {}
     verify(withSpan).close();
-    verify(span).end(same(EndSpanOptions.getDefault()));
+    verify(span).end(same(EndSpanOptions.DEFAULT));
   }
 
   @Test
@@ -243,7 +243,7 @@ public class TracerTest {
     when(contextSpanHandler.withSpan(same(span))).thenReturn(withSpan);
     try (NonThrowingCloseable ss = mockTracer.startScopedSpan("MySpanName", startSpanOptions)) {}
     verify(withSpan).close();
-    verify(span).end(same(EndSpanOptions.getDefault()));
+    verify(span).end(same(EndSpanOptions.DEFAULT));
   }
 
   @Test
@@ -254,7 +254,7 @@ public class TracerTest {
     when(contextSpanHandler.withSpan(same(span))).thenReturn(withSpan);
     try (NonThrowingCloseable ss = mockTracer.startScopedSpan(span, "MySpanName")) {}
     verify(withSpan).close();
-    verify(span).end(same(EndSpanOptions.getDefault()));
+    verify(span).end(same(EndSpanOptions.DEFAULT));
   }
 
   @Test
@@ -267,7 +267,7 @@ public class TracerTest {
     try (NonThrowingCloseable ss =
         mockTracer.startScopedSpan(span, "MySpanName", startSpanOptions)) {}
     verify(withSpan).close();
-    verify(span).end(same(EndSpanOptions.getDefault()));
+    verify(span).end(same(EndSpanOptions.DEFAULT));
   }
 
   @Test
@@ -291,7 +291,8 @@ public class TracerTest {
   @Test
   public void startSpanWitRemoteParent() {
     Tracer mockTracer = newTracerWithMocks();
-    SpanContext spanContext = new SpanContext(new TraceId(10, 20), 30, TraceOptions.getDefault());
+    SpanContext spanContext = new SpanContext(new TraceId(10, 20), new SpanId(30),
+        TraceOptions.getDefault());
     StartSpanOptions startSpanOptions = StartSpanOptions.builder().build();
     when(spanFactory.startSpanWithRemoteParent(
             same(spanContext), eq("MySpanName"), same(startSpanOptions)))