CommitMsgHookTest: Simplify Win32 platform avoidance

Instead of testing for Win32 platform in the @Before annotated method
that is called before every test, add a new method annotated with
@BeforeClass that will skip the entire test suite when the platform
is Win32.

Also use the assume() method from Google Truth which has an isFalse()
method, rather than using assumeTrue() with reverse logic.

Change-Id: Ia14e4dcb7d7136ca6568a9a906a2293a9c75b329

gerrit-server/src/test/java/com/google/gerrit/server/tools/hooks/CommitMsgHookTest.java

@@ -14,10 +14,10 @@
 
 package com.google.gerrit.server.tools.hooks;
 
+import static com.google.common.truth.TruthJUnit.assume;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
-import static org.junit.Assume.assumeTrue;
 
 import com.google.gerrit.server.util.HostPlatform;
 
@@ -31,9 +31,8 @@ import org.eclipse.jgit.lib.ObjectInserter;
 import org.eclipse.jgit.lib.PersonIdent;
 import org.eclipse.jgit.lib.RefUpdate;
 import org.junit.Before;
-import org.junit.Rule;
+import org.junit.BeforeClass;
 import org.junit.Test;
-import org.junit.rules.TestName;
 
 import java.io.File;
 import java.io.IOException;
@@ -44,20 +43,14 @@ public class CommitMsgHookTest extends HookTestCase {
   private final String SOB1 = "Signed-off-by: J Author <ja@example.com>\n";
   private final String SOB2 = "Signed-off-by: J Committer <jc@example.com>\n";
 
-  @Rule public TestName test = new TestName();
-
-  private void skipIfWin32Platform() {
-    if (HostPlatform.isWin32()) {
-      System.err.println(" - Skipping " + test.getMethodName() + " on this system");
-      assumeTrue(false);
-    }
+  @BeforeClass
+  public static void skipIfWin32Platform() {
+    assume().that(HostPlatform.isWin32()).isFalse();
   }
 
   @Override
   @Before
   public void setUp() throws Exception {
-    skipIfWin32Platform();
-
     super.setUp();
     final Date when = author.getWhen();
     final TimeZone tz = author.getTimeZone();