[rm-first-char] remove the first char from a string (#663)

Author: sk1418

core-kotlin-modules/core-kotlin-strings-3/src/test/kotlin/com/baeldung/removeTheFirstChar/RemoveTheFirstCharUnitTest.kt

@@ -0,0 +1,59 @@
+package com.baeldung.removeTheFirstChar
+
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+import kotlin.test.assertEquals
+
+class RemoveTheFirstCharUnitTest {
+
+    @Test
+    fun `when calling drop() then get the expected result`() {
+        val myStr = "0a b c d e"
+        val result = myStr.drop(1)
+        assertEquals("a b c d e", result)
+
+        //works when the string is empty
+        val result2 = "".drop(1)
+        assertEquals("", result2)
+    }
+
+    @Test
+    fun `when calling subString() then get the expected result`() {
+        val myStr = "0a b c d e"
+        val result = myStr.substring(1)
+        assertEquals("a b c d e", result)
+
+        //throw exception when the string is empty
+        assertThrows<IndexOutOfBoundsException> {
+            "".substring(1)
+        }
+    }
+
+    @Test
+    fun `when calling takeLast() then get the expected result`() {
+        val myStr = "0a b c d e"
+        val result = myStr.takeLast(myStr.length - 1) // or takeLast(myStr.lastIndex)
+        assertEquals("a b c d e", result)
+
+        //works when the string is empty
+        val myEmpty = ""
+
+        assertThrows<IllegalArgumentException> {
+            myEmpty.takeLast(myEmpty.length - 1)
+        }.also {
+            assertEquals("Requested character count -1 is less than zero.", it.message)
+        }
+
+    }
+
+    @Test
+    fun `when using replace() then get the expected result`() {
+        val myStr = "0a b c d e"
+        val result = myStr.replace("^.".toRegex(), "")
+        assertEquals("a b c d e", result)
+
+        //works when the string is empty
+        val result2 = "".replace("^.".toRegex(), "")
+        assertEquals("", result2)
+    }
+}