Adding a simple unit test for EmptyResponseProcessor.

Data/src/main/java/org/tribuo/data/columnar/processors/response/EmptyResponseProcessor.java

@@ -34,7 +34,7 @@
  *  It still requires an output factory, even though it's never used to generate
  *  an output, because the output factory provides the type for the columnar infrastructure.
  */
-public class EmptyResponseProcessor<T extends Output<T>> implements ResponseProcessor<T> {
+public final class EmptyResponseProcessor<T extends Output<T>> implements ResponseProcessor<T> {
 
     public static final String FIELD_NAME = "TRIBUO##NULL_RESPONSE_PROCESSOR";
 

Data/src/test/java/org/tribuo/data/columnar/processors/response/EmptyResponseProcessorTest.java

@@ -0,0 +1,34 @@
+package org.tribuo.data.columnar.processors.response;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.tribuo.test.MockOutput;
+import org.tribuo.test.MockOutputFactory;
+
+public class EmptyResponseProcessorTest {
+
+    @Test
+    public void basicTest() {
+        MockOutputFactory outputFactory = new MockOutputFactory();
+        EmptyResponseProcessor<MockOutput> rp = new EmptyResponseProcessor<>(outputFactory);
+
+        // Check the output factory is stored correctly
+        Assertions.assertEquals(outputFactory,rp.getOutputFactory());
+
+        // Check the field name is right
+        Assertions.assertEquals(EmptyResponseProcessor.FIELD_NAME, rp.getFieldName());
+
+        // setFieldName is a no-op on this response processor
+        rp.setFieldName("Something");
+        Assertions.assertEquals(EmptyResponseProcessor.FIELD_NAME, rp.getFieldName());
+
+        // Check that it doesn't throw exceptions when given odd text, and that it always returns Optional.empty.
+        Assertions.assertFalse(rp.process("").isPresent());
+        Assertions.assertFalse(rp.process("test").isPresent());
+        Assertions.assertFalse(rp.process("!@$#$!").isPresent());
+        Assertions.assertFalse(rp.process("\n").isPresent());
+        Assertions.assertFalse(rp.process("\t").isPresent());
+        Assertions.assertFalse(rp.process(null).isPresent());
+    }
+
+}