Add abstract utility class for working with java.util.function.Functions.

spring-geode/src/test/java/org/springframework/geode/core/util/function/FunctionUtilsUnitTests.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+package org.springframework.geode.core.util.function;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+import java.util.function.Consumer;
+import java.util.function.Function;
+
+import org.junit.Test;
+
+/**
+ * Unit Tests for {@link FunctionUtils}.
+ *
+ * @author John Blum
+ * @see java.util.function.Consumer
+ * @see java.util.function.Function
+ * @see org.junit.Test
+ * @see org.mockito.Mockito
+ * @since 1.1.0
+ */
+public class FunctionUtilsUnitTests {
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void callsConsumerReturnsNull() {
+
+		Consumer<Object> mockConsumer = mock(Consumer.class);
+
+		Function<Object, Object> function = FunctionUtils.toNullReturningFunction(mockConsumer);
+
+		assertThat(function).isNotNull();
+		assertThat(function.apply("test")).isNull();
+
+		verify(mockConsumer, times(1)).accept(eq("test"));
+	}
+}