KTLN-639: Check If a Character is Alphabet or Not in Kotlin (#584)

* Unit tests

* Code fixes

* code fixes

Author: nappy29

core-kotlin-modules/core-kotlin-8/src/test/kotlin/com/baeldung/alphabetcheck/CheckAlphabetUnitTest.kt

@@ -0,0 +1,80 @@
+package com.baeldung.alphabetcheck
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class CheckAlphabetUnitTest {
+
+    @Test
+    fun `check using isLetter() method`() {
+        assertTrue('a'.isLetter())
+        assertTrue('w'.isLetter())
+        assertTrue('T'.isLetter())
+        assertTrue('P'.isLetter())
+        assertFalse('%'.isLetter())
+        assertFalse('4'.isLetter())
+        assertFalse('.'.isLetter())
+        assertFalse('*'.isLetter())
+    }
+
+    @Test
+    fun `check using range method`() {
+        assertTrue(usingRangeMethod('a'))
+        assertTrue(usingRangeMethod('w'))
+        assertTrue(usingRangeMethod('T'))
+        assertTrue(usingRangeMethod('P'))
+        assertFalse(usingRangeMethod('%'))
+        assertFalse(usingRangeMethod('4'))
+        assertFalse(usingRangeMethod('.'))
+        assertFalse(usingRangeMethod('*'))
+    }
+
+    @Test
+    fun `check using regex method`() {
+        assertTrue(usingRegexMethod('a'))
+        assertTrue(usingRegexMethod('w'))
+        assertTrue(usingRegexMethod('T'))
+        assertTrue(usingRegexMethod('P'))
+        assertFalse(usingRegexMethod('%'))
+        assertFalse(usingRegexMethod('4'))
+        assertFalse(usingRegexMethod('.'))
+        assertFalse(usingRegexMethod('*'))
+    }
+
+    @Test
+    fun `check using isAlphabetic method`() {
+        assertTrue(Character.isAlphabetic('a'.code))
+        assertTrue(Character.isAlphabetic('w'.code))
+        assertTrue(Character.isAlphabetic('T'.code))
+        assertTrue(Character.isAlphabetic('P'.code))
+        assertFalse(Character.isAlphabetic('%'.code))
+        assertFalse(Character.isAlphabetic('4'.code))
+        assertFalse(Character.isAlphabetic('.'.code))
+        assertFalse(Character.isAlphabetic('*'.code))
+    }
+
+    @Test
+    fun `check using ASCII method`() {
+        assertTrue(usingAsciiValues('a'))
+        assertTrue(usingAsciiValues('w'))
+        assertTrue(usingAsciiValues('T'))
+        assertTrue(usingAsciiValues('P'))
+        assertFalse(usingAsciiValues('%'))
+        assertFalse(usingAsciiValues('4'))
+        assertFalse(usingAsciiValues('.'))
+        assertFalse(usingAsciiValues('*'))
+    }
+
+    fun usingRangeMethod(ch: Char): Boolean {
+        return ch in 'A'..'Z' || ch in 'a'..'z'
+    }
+
+    fun usingRegexMethod(ch: Char): Boolean {
+        return ch.toString().matches("[a-zA-Z]".toRegex())
+    }
+
+    fun usingAsciiValues(ch: Char): Boolean {
+        return (ch.code in 65..90) || (ch.code in 97..122)
+    }
+}