diff --git a/javatests/com/google/re2j/CharClassTest.java b/javatests/com/google/re2j/CharClassTest.java
index 00eea0b3..faceb1fa 100644
--- a/javatests/com/google/re2j/CharClassTest.java
+++ b/javatests/com/google/re2j/CharClassTest.java
@@ -7,13 +7,14 @@
 package com.google.re2j;
 
 import static com.google.re2j.Utils.stringToRunes;
-
 import static org.junit.Assert.assertEquals;
 
 import java.util.Arrays;
-
 import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
 
+@RunWith(JUnit4.class)
 public class CharClassTest {
 
   private static CharClass cc(int... x) {
diff --git a/javatests/com/google/re2j/ParserTest.java b/javatests/com/google/re2j/ParserTest.java
index 87cd152a..a97b7599 100644
--- a/javatests/com/google/re2j/ParserTest.java
+++ b/javatests/com/google/re2j/ParserTest.java
@@ -21,16 +21,18 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.fail;
 
+import com.google.common.truth.Truth;
 import java.util.ArrayList;
 import java.util.EnumMap;
 import java.util.Map;
-
-import com.google.common.truth.Truth;
 import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
 
 /**
  * @author adonovan@google.com (Alan Donovan)
  */
+@RunWith(JUnit4.class)
 public class ParserTest {
 
   private interface RunePredicate {
@@ -405,6 +407,8 @@ private static void dumpRegexp(StringBuilder b, Regexp re) {
     }
     b.append('{');
     switch (re.op) {
+      default:
+        break;
       case END_TEXT:
         if ((re.flags & WAS_DOLLAR) == 0) {
           b.append("\\z");
@@ -583,7 +587,7 @@ public void testParseInvalidRegexps() throws PatternSyntaxException {
       }
     }
     for (String regexp : ONLY_PERL) {
-      Parser.parse(regexp, PERL);
+      Regexp unused = Parser.parse(regexp, PERL);
       try {
         Regexp re = Parser.parse(regexp, POSIX);
         fail("parsing (POSIX) " + regexp + " should have failed, instead got " + dump(re));
@@ -598,7 +602,7 @@ public void testParseInvalidRegexps() throws PatternSyntaxException {
       } catch (PatternSyntaxException e) {
         /* ok */
       }
-      Parser.parse(regexp, POSIX);
+      Regexp unused = Parser.parse(regexp, POSIX);
     }
   }
 
diff --git a/javatests/com/google/re2j/RE2CompileTest.java b/javatests/com/google/re2j/RE2CompileTest.java
index 0ac6294d..916b4002 100644
--- a/javatests/com/google/re2j/RE2CompileTest.java
+++ b/javatests/com/google/re2j/RE2CompileTest.java
@@ -67,7 +67,7 @@ public RE2CompileTest(String input, String expectedError) {
   @Test
   public void testCompile() {
     try {
-      RE2.compile(input);
+      RE2 unused = RE2.compile(input);
       if (expectedError != null) {
         fail("RE2.compile(" + input + ") was successful, expected " + expectedError);
       }
diff --git a/javatests/com/google/re2j/RE2Test.java b/javatests/com/google/re2j/RE2Test.java
index cb204dfd..cf30b3a3 100644
--- a/javatests/com/google/re2j/RE2Test.java
+++ b/javatests/com/google/re2j/RE2Test.java
@@ -9,13 +9,16 @@
 
 package com.google.re2j;
 
-import java.util.Arrays;
-import org.junit.Test;
-
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
+import java.util.Arrays;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
 /** Tests of RE2 API. */
+@RunWith(JUnit4.class)
 public class RE2Test {
   @Test
   public void testFullMatch() {
diff --git a/javatests/com/google/re2j/UnicodeTest.java b/javatests/com/google/re2j/UnicodeTest.java
index 8309e4ef..58ee79eb 100644
--- a/javatests/com/google/re2j/UnicodeTest.java
+++ b/javatests/com/google/re2j/UnicodeTest.java
@@ -6,13 +6,15 @@
  */
 package com.google.re2j;
 
-import org.junit.Test;
+import static org.junit.Assert.*;
 
 import java.util.ArrayList;
 import java.util.List;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
 
-import static org.junit.Assert.*;
-
+@RunWith(JUnit4.class)
 public class UnicodeTest {
 
   @Test