add performance test

core-kotlin/src/test/kotlin/com/baeldung/random/RandomStringTest.kt

@@ -1,52 +1,70 @@
 import org.apache.commons.lang3.RandomStringUtils
+import org.junit.Before
+import org.junit.jupiter.api.BeforeAll
+import org.junit.jupiter.api.BeforeEach
 import org.junit.jupiter.api.Test
+import java.security.SecureRandom
 import java.util.concurrent.ThreadLocalRandom
+import kotlin.experimental.and
 import kotlin.streams.asSequence
 import kotlin.test.assertEquals
 
-const val STRING_LENGTH = 10;
-const val ALPHANUMERIC_REGEX = "[a-zA-Z0-9]+";
+const val STRING_LENGTH = 10
+const val ALPHANUMERIC_REGEX = "[a-zA-Z0-9]+"
 
 class RandomStringTest {
 
-    @Test
-    fun generateRandomString_useJava_returnString() {
-        val charPool = ArrayList<Char>();
+    val charPool = ArrayList<Char>()
+
+    @BeforeEach
+    fun charPool() {
         charPool.addAll('a'..'z');
         charPool.addAll('A'..'Z');
         charPool.addAll('0'..'9');
+    }
 
+    @Test
+    fun givenAStringLength_whenUsingJava_thenReturnAlphanumericString() {
         var randomString = ThreadLocalRandom.current()
                 .ints(STRING_LENGTH.toLong(), 0, charPool.size)
                 .asSequence()
                 .map(charPool::get)
                 .joinToString("")
 
-        assert(randomString.matches(Regex(ALPHANUMERIC_REGEX)));
-        assertEquals(STRING_LENGTH, randomString.length);
+        assert(randomString.matches(Regex(ALPHANUMERIC_REGEX)))
+        assertEquals(STRING_LENGTH, randomString.length)
     }
 
     @Test
-    fun generateRandomString_useKotlin_returnString() {
-        val charPool = ArrayList<Char>();
-        charPool.addAll('a'..'z');
-        charPool.addAll('A'..'Z');
-        charPool.addAll('0'..'9');
-
+    fun givenAStringLength_whenUsingKotlin_thenReturnAlphanumericString() {
         var randomString = (1..STRING_LENGTH).map { i -> kotlin.random.Random.nextInt(0, charPool.size) }
                 .map(charPool::get)
-                .joinToString("");
+                .joinToString("")
 
-        assert(randomString.matches(Regex(ALPHANUMERIC_REGEX)));
-        assertEquals(STRING_LENGTH, randomString.length);
+        assert(randomString.matches(Regex(ALPHANUMERIC_REGEX)))
+        assertEquals(STRING_LENGTH, randomString.length)
     }
 
     @Test
-    fun generateRandomString_useApacheCommon_returnString() {
-        var randomString = RandomStringUtils.randomAlphanumeric(STRING_LENGTH);
+    fun givenAStringLength_whenUsingApacheCommon_thenReturnAlphanumericString() {
+        var randomString = RandomStringUtils.randomAlphanumeric(STRING_LENGTH)
 
-        assert(randomString.matches(Regex(ALPHANUMERIC_REGEX)));
-        assertEquals(STRING_LENGTH, randomString.length);
+        assert(randomString.matches(Regex(ALPHANUMERIC_REGEX)))
+        assertEquals(STRING_LENGTH, randomString.length)
+    }
+
+    @Test
+    fun givenAStringLength_whenUsingRandomForBytes_thenReturnAlphanumericString() {
+        val random = SecureRandom()
+        val bytes = ByteArray(STRING_LENGTH)
+        random.nextBytes(bytes)
+
+        var randomString = (0..bytes.size - 1).map { i ->
+            charPool.get((bytes[i] and 0xFF.toByte() and charPool.size.toByte()).toInt())
+        }.joinToString("")
+
+        assert(randomString.matches(Regex(ALPHANUMERIC_REGEX)))
+        assertEquals(STRING_LENGTH, randomString.length)
     }
 
 }