Fix Coder.Context equality and hashCode

This only worked if you depended on the instances directly and didn't construct your own.
Also add Coder.Context#toString()

----Release Notes----

[]
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112736780

Author: lukecwik

sdk/src/main/java/com/google/cloud/dataflow/sdk/coders/Coder.java

@@ -21,6 +21,8 @@
 import com.google.cloud.dataflow.sdk.util.CloudObject;
 import com.google.cloud.dataflow.sdk.util.common.ElementByteSizeObserver;
 import com.google.common.base.Joiner;
+import com.google.common.base.MoreObjects;
+import com.google.common.base.Objects;
 import com.google.common.base.Preconditions;
 
 import java.io.IOException;
@@ -30,7 +32,6 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
-import java.util.Objects;
 
 import javax.annotation.Nullable;
 
@@ -92,6 +93,25 @@ public Context(boolean isWholeStream) {
     public Context nested() {
       return NESTED;
     }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (!(obj instanceof Context)) {
+        return false;
+      }
+      return Objects.equal(isWholeStream, ((Context) obj).isWholeStream);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hashCode(isWholeStream);
+    }
+
+    @Override
+    public String toString() {
+      return MoreObjects.toStringHelper(Context.class)
+          .addValue(isWholeStream ? "OUTER" : "NESTED").toString();
+    }
   }
 
   /**

sdk/src/test/java/com/google/cloud/dataflow/sdk/coders/CoderTest.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright (C) 2016 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.cloud.dataflow.sdk.coders;
+
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.containsString;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertThat;
+
+import com.google.cloud.dataflow.sdk.coders.Coder.Context;
+import com.google.cloud.dataflow.sdk.coders.Coder.NonDeterministicException;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+import java.util.Collections;
+
+/** Tests for constructs defined within {@link Coder}. */
+@RunWith(JUnit4.class)
+public class CoderTest {
+  @Rule public ExpectedException expectedException = ExpectedException.none();
+
+  @Test
+  public void testContextEqualsAndHashCode() {
+    assertEquals(Context.NESTED, new Context(false));
+    assertEquals(Context.OUTER, new Context(true));
+    assertNotEquals(Context.NESTED, Context.OUTER);
+
+    assertEquals(Context.NESTED.hashCode(), new Context(false).hashCode());
+    assertEquals(Context.OUTER.hashCode(), new Context(true).hashCode());
+    // Even though this isn't strictly required by the hashCode contract,
+    // we still want this to be true.
+    assertNotEquals(Context.NESTED.hashCode(), Context.OUTER.hashCode());
+  }
+
+  @Test
+  public void testContextToString() {
+    assertEquals("Context{NESTED}", Context.NESTED.toString());
+    assertEquals("Context{OUTER}", Context.OUTER.toString());
+  }
+
+  @Test
+  public void testNonDeterministicExcpetionRequiresReason() {
+    expectedException.expect(IllegalArgumentException.class);
+    expectedException.expectMessage("Reasons must not be empty");
+    new NonDeterministicException(VoidCoder.of(), Collections.<String>emptyList());
+  }
+
+  @Test
+  public void testNonDeterministicException() {
+    NonDeterministicException rootCause =
+        new NonDeterministicException(VoidCoder.of(), "Root Cause");
+    NonDeterministicException exception =
+        new NonDeterministicException(StringUtf8Coder.of(), "Problem", rootCause);
+    assertEquals(rootCause, exception.getCause());
+    assertThat(exception.getReasons(), contains("Problem"));
+    assertThat(exception.toString(), containsString("Problem"));
+    assertThat(exception.toString(), containsString("is not deterministic"));
+  }
+}
+