Added BiFunction section

Author: sagaofsilence

core-java/functional-programming/functional-interfaces/src/test/java/io/reflectoring/function/FunctionTest.java

@@ -0,0 +1,42 @@
+package io.reflectoring.function;
+
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class FunctionTest {
+
+  @Test
+  void simpleFunction() {
+    Function<String, String> toUpper = s -> s == null ? null : s.toUpperCase();
+    Assertions.assertEquals("JOY", toUpper.apply("joy"));
+    Assertions.assertNull(toUpper.apply(null));
+  }
+
+  @Test
+  void functionComposition() {
+    Function<String, String> toUpper = s -> s == null ? null : s.toUpperCase();
+    Function<String, String> replaceVowels =
+        s ->
+            s == null
+                ? null
+                : s.replace("A", "")
+                    .replace("E", "")
+                    .replace("I", "")
+                    .replace("O", "")
+                    .replace("U", "");
+    Assertions.assertEquals("APPLE", toUpper.compose(replaceVowels).apply("apple"));
+    Assertions.assertEquals("PPL", toUpper.andThen(replaceVowels).apply("apple"));
+  }
+
+  @Test
+  void biFunction() {
+    BiFunction<Integer, Integer, Integer> bigger =
+        (first, second) -> first > second ? first : second;
+    Function<Integer, Integer> square = number -> number * number;
+
+    Assertions.assertEquals(10, bigger.apply(4, 10));
+    Assertions.assertEquals(100, bigger.andThen(square).apply(4, 10));
+  }
+}

core-java/functional-programming/functional-interfaces/src/test/java/io/reflectoring/function/predicate/PredicateTest.java renamed to core-java/functional-programming/functional-interfaces/src/test/java/io/reflectoring/function/PredicateTest.java

@@ -1,16 +1,14 @@
-package io.reflectoring.function.predicate;
+package io.reflectoring.function;
 
 import java.util.Arrays;
 import java.util.List;
 import java.util.function.*;
 import java.util.stream.DoubleStream;
 import java.util.stream.IntStream;
 import java.util.stream.LongStream;
-import lombok.extern.slf4j.Slf4j;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
-@Slf4j
 public class PredicateTest {
   // C = Carpenter, W = Welder
   private final Object[][] workers = {