Add FindMaxRecursionTest (#4431)

* Update FindMaxRecursion.java

* Create FindMaxRecusionTest.java

* Update and rename FindMaxRecusionTest.java to FindMaxRecursionTest.java

* Update FindMaxRecursion.java

* Update FindMaxRecursion.java

* Update src/test/java/com/thealgorithms/maths/FindMaxRecursionTest.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/test/java/com/thealgorithms/maths/FindMaxRecursionTest.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update src/main/java/com/thealgorithms/maths/FindMaxRecursion.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update FindMaxRecursion.java

* Update FindMaxRecursionTest.java

* Update FindMaxRecursionTest.java

* Update FindMaxRecursion.java

* Update src/main/java/com/thealgorithms/maths/FindMaxRecursion.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

* Update FindMaxRecursion.java

* Update FindMaxRecursion.java

* Update FindMaxRecursion.java

* Update FindMaxRecursion.java

* Update FindMaxRecursion.java

* Update src/main/java/com/thealgorithms/maths/FindMaxRecursion.java

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

---------

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

src/main/java/com/thealgorithms/maths/FindMaxRecursion.java

@@ -1,26 +1,9 @@
 package com.thealgorithms.maths;
 
-import java.util.Arrays;
-import java.util.Random;
+public final class FindMaxRecursion {
 
-public class FindMaxRecursion {
-
-    public static void main(String[] args) {
-        Random rand = new Random();
-
-        /* rand size */
-        int size = rand.nextInt(100) + 1;
-        int[] array = new int[size];
-
-        /* init array with rand numbers */
-        for (int i = 0; i < size; i++) {
-            array[i] = rand.nextInt() % 100;
-        }
-
-        assert max(array) == Arrays.stream(array).max().getAsInt();
-        assert max(array, 0, array.length - 1) == Arrays.stream(array).max().getAsInt();
+    private FindMaxRecursion() {
     }
-
     /**
      * Get max of array using divide and conquer algorithm
      *
@@ -29,7 +12,10 @@ public class FindMaxRecursion {
      * @param high the index of the last element
      * @return max of {@code array}
      */
-    public static int max(int[] array, int low, int high) {
+    public static int max(final int[] array, final int low, final int high) {
+        if (array.length == 0) {
+            throw new IllegalArgumentException("array must be non-empty.");
+        }
         if (low == high) {
             return array[low]; // or array[high]
         }
@@ -48,7 +34,7 @@ public class FindMaxRecursion {
      * @param array contains elements
      * @return max value of {@code array}
      */
-    public static int max(int[] array) {
-        return array.length == 1 ? array[0] : max(array, 0, array.length);
+    public static int max(final int[] array) {
+        return max(array, 0, array.length - 1);
     }
 }

src/test/java/com/thealgorithms/maths/FindMaxRecursionTest.java

@@ -0,0 +1,28 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class FindMaxRecursionTest {
+
+    @ParameterizedTest
+    @MethodSource("inputStream")
+    void numberTests(int expected, int[] input) {
+        Assertions.assertEquals(expected, FindMaxRecursion.max(input));
+    }
+
+    private static Stream<Arguments> inputStream() {
+        return Stream.of(Arguments.of(5, new int[] {5, 5, 5, 5, 5}), Arguments.of(0, new int[] {-1, 0}), Arguments.of(-1, new int[] {-10, -9, -8, -7, -6, -5, -4, -3, -2, -1}), Arguments.of(9, new int[] {3, -2, 3, 9, -4, -4, 8}), Arguments.of(3, new int[] {3}));
+    }
+
+    @Test
+    public void testFindMaxThrowsExceptionForEmptyInput() {
+        assertThrows(IllegalArgumentException.class, () -> FindMaxRecursion.max(new int[] {}));
+    }
+}