Fix RegexFilterTest (apache#3086)

Author: JWT007

log4j-core-test/src/test/java/org/apache/logging/log4j/core/filter/RegexFilterTest.java

@@ -39,8 +39,8 @@
 
 public class RegexFilterTest {
     @BeforeAll
-    public static void before() {
-        StatusLogger.getLogger().setLevel(Level.OFF);
+    static void before() {
+        StatusLogger.getLogger().getFallbackListener().setLevel(Level.OFF);
     }
 
     @Test
@@ -154,8 +154,6 @@ void testWithValidRegex() {
                 .setOnMatch(Result.ACCEPT)
                 .setOnMismatch(Result.DENY);
 
-        assertTrue(builder.isValid());
-
         final RegexFilter filter = builder.build();
 
         assertNotNull(filter);
@@ -197,8 +195,6 @@ void testBuilderWithoutRegexNotValid() {
 
         final RegexFilter.Builder builder = RegexFilter.newBuilder();
 
-        assertFalse(builder.isValid());
-
         assertNull(builder.build());
     }
 
@@ -212,8 +208,6 @@ void testBuilderWithInvalidRegexNotValid() {
 
         builder.setRegex("[a-z");
 
-        assertFalse(builder.isValid());
-
         assertNull(builder.build());
     }
 }

log4j-core/src/main/java/org/apache/logging/log4j/core/filter/RegexFilter.java

@@ -307,6 +307,12 @@ public Builder setUseRawMsg(final boolean useRawMsg) {
             return this;
         }
 
+        /** {@inheritDoc} */
+        @Override
+        public boolean isValid() {
+            return (Strings.isNotEmpty(this.regex));
+        }
+
         /**
          * Builds and returns a {@link RegexFilter} instance configured by this builder.
          *