diff --git a/core-java-collections/src/test/java/org/baeldung/java/collections/CollectionsEmpty.java b/core-java-collections/src/test/java/org/baeldung/java/collections/CollectionsEmpty.java
new file mode 100644
index 0000000000..09ecebe47b
--- /dev/null
+++ b/core-java-collections/src/test/java/org/baeldung/java/collections/CollectionsEmpty.java
@@ -0,0 +1,26 @@
+package org.baeldung.java.collections;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import org.junit.Assert;
+import org.junit.Test;
+
+class CollectionsEmpty {
+
+    @Test
+    public void givenArrayList_whenAddingElement_addsNewElement() {
+        ArrayList<String> mutableList = new ArrayList<>();
+        mutableList.add("test");
+
+        Assert.assertEquals(mutableList.size(), 1);
+        Assert.assertEquals(mutableList.get(0), "test");
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
+    public void givenCollectionsEmptyList_whenAddingElement_throwsUnsupportedOperationException() {
+        List<String> immutableList = Collections.emptyList();
+        immutableList.add("test");
+    }
+
+}
diff --git a/core-kotlin/src/test/kotlin/com/baeldung/random/RandomNumberTest.kt b/core-kotlin/src/test/kotlin/com/baeldung/random/RandomNumberTest.kt
new file mode 100644
index 0000000000..2956a35f8a
--- /dev/null
+++ b/core-kotlin/src/test/kotlin/com/baeldung/random/RandomNumberTest.kt
@@ -0,0 +1,55 @@
+
+import org.junit.jupiter.api.Test
+import java.util.concurrent.ThreadLocalRandom
+import kotlin.test.assertTrue
+
+class RandomNumberTest {
+
+    @Test
+    fun whenRandomNumberWithJavaUtilMath_thenResultIsBetween0And1() {
+        val randomNumber = Math.random()
+        assertTrue { randomNumber >=0 }
+        assertTrue { randomNumber <= 1 }
+    }
+
+    @Test
+    fun whenRandomNumberWithJavaThreadLocalRandom_thenResultsInDefaultRanges() {
+        val randomDouble = ThreadLocalRandom.current().nextDouble()
+        val randomInteger = ThreadLocalRandom.current().nextInt()
+        val randomLong = ThreadLocalRandom.current().nextLong()
+        assertTrue { randomDouble >= 0 }
+        assertTrue { randomDouble <= 1 }
+        assertTrue { randomInteger >= Integer.MIN_VALUE }
+        assertTrue { randomInteger <= Integer.MAX_VALUE }
+        assertTrue { randomLong >= Long.MIN_VALUE }
+        assertTrue { randomLong <= Long.MAX_VALUE }
+    }
+
+    @Test
+    fun whenRandomNumberWithKotlinJSMath_thenResultIsBetween0And1() {
+        val randomDouble = Math.random()
+        assertTrue { randomDouble >=0 }
+        assertTrue { randomDouble <= 1 }
+    }
+
+    @Test
+    fun whenRandomNumberWithKotlinNumberRange_thenResultInGivenRange() {
+        val randomInteger = (1..12).shuffled().first()
+        assertTrue { randomInteger >= 1 }
+        assertTrue { randomInteger <= 12 }
+    }
+
+    @Test
+    fun whenRandomNumberWithJavaThreadLocalRandom_thenResultsInGivenRanges() {
+        val randomDouble = ThreadLocalRandom.current().nextDouble(1.0, 10.0)
+        val randomInteger = ThreadLocalRandom.current().nextInt(1, 10)
+        val randomLong = ThreadLocalRandom.current().nextLong(1, 10)
+        assertTrue { randomDouble >= 1 }
+        assertTrue { randomDouble <= 10 }
+        assertTrue { randomInteger >= 1 }
+        assertTrue { randomInteger <= 10 }
+        assertTrue { randomLong >= 1 }
+        assertTrue { randomLong <= 10 }
+    }
+
+}
\ No newline at end of file
diff --git a/spring-5-reactive/src/main/java/com/baeldung/reactive/util/CpuUtils.java b/spring-5-reactive/src/main/java/com/baeldung/reactive/util/CpuUtils.java
new file mode 100644
index 0000000000..8d16434920
--- /dev/null
+++ b/spring-5-reactive/src/main/java/com/baeldung/reactive/util/CpuUtils.java
@@ -0,0 +1,15 @@
+package com.baeldung.reactive.util;
+
+import com.sun.management.OperatingSystemMXBean;
+
+import java.lang.management.ManagementFactory;
+
+public class CpuUtils {
+
+    private static OperatingSystemMXBean operatingSystemMXBean = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
+
+    static Double getUsage() {
+        return (operatingSystemMXBean.getSystemCpuLoad() / operatingSystemMXBean.getAvailableProcessors()) * 100;
+    }
+
+}