Add MaxValueTest and remove main from MaxValue (#4756)

* Create MaxValueTest.java

* Update MaxValue.java

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

@@ -0,0 +1,14 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class MaxValueTest {
+    @Test
+    public void maxTest() {
+        assertEquals(-1, MaxValue.max(-1, -3));
+        assertEquals(3, MaxValue.max(3, 2));
+        assertEquals(5, MaxValue.max(5, 5));
+    }
+}