Test alphabetical (#2987)

src/test/java/com/thealgorithms/strings/AlphabeticalTest.java

@@ -0,0 +1,30 @@
+package com.thealgorithms.strings;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+
+public class AlphabeticalTest {
+    @Test
+    public void isAlphabetical() {
+        // expected to be true
+        String input1 = "abcdefghijklmno";
+        String input2 = "abcdxxxyzzzz";
+        String input3 = "fpw";
+
+        // expected to be false
+        String input4 = "123a";
+        String input5 = "abcABC";
+        String input6 = "abcdefghikjlmno";
+
+        assertTrue(Alphabetical.isAlphabetical(input1));
+        assertTrue(Alphabetical.isAlphabetical(input2));
+        assertTrue(Alphabetical.isAlphabetical(input3));
+
+        assertFalse(Alphabetical.isAlphabetical(input4));
+        assertFalse(Alphabetical.isAlphabetical(input5));
+        assertFalse(Alphabetical.isAlphabetical(input6));
+    }
+
+}