Fill in the test coverage for getAllowDuplicateHeaderNames() to reflect

the _current_ behavior, right or wrong.

Author: garydgregory

src/test/java/org/apache/commons/csv/CSVFormatTest.java

@@ -45,6 +45,7 @@
 import java.util.Arrays;
 import java.util.Objects;
 
+import org.apache.commons.csv.CSVFormat.Builder;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
@@ -1168,6 +1169,15 @@ public void testWithEmptyDuplicates() {
         assertFalse(formatWithEmptyDuplicates.getAllowDuplicateHeaderNames());
     }
 
+    @Test
+    public void testGetAllowDuplicateHeaderNames() {
+        final Builder builder = CSVFormat.DEFAULT.builder();
+        assertTrue(builder.build().getAllowDuplicateHeaderNames());
+        assertTrue(builder.setDuplicateHeaderMode(DuplicateHeaderMode.ALLOW_ALL).build().getAllowDuplicateHeaderNames());
+        assertFalse(builder.setDuplicateHeaderMode(DuplicateHeaderMode.ALLOW_EMPTY).build().getAllowDuplicateHeaderNames());
+        assertFalse(builder.setDuplicateHeaderMode(DuplicateHeaderMode.DISALLOW).build().getAllowDuplicateHeaderNames());
+    }
+
     @Test
     public void testWithEmptyEnum() {
         final CSVFormat formatWithHeader = CSVFormat.DEFAULT.withHeader(EmptyEnum.class);