[Update] resolve after review

core-java-modules/core-java-uuid/src/test/java/com/baeldung/uuid/UUIDLongGeneratorUnitTest.java

@@ -0,0 +1,60 @@
+package com.baeldung.uuid;
+
+import org.apache.log4j.Logger;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.text.DecimalFormat;
+import java.util.HashSet;
+import java.util.Set;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class UUIDLongGeneratorUnitTest {
+    private final static int n = 1000000;
+    private final static double COLLISION_THRESHOLD = 0.001;
+    private static final Logger logger = Logger.getLogger(UUIDLongGeneratorUnitTest.class);
+    private final UUIDPositiveLongGenerator uuidLongGenerator = new UUIDPositiveLongGenerator();
+
+    @Test
+    void whenForeachGenerateLongValue_thenCollisionsCheck() throws InvocationTargetException, IllegalAccessException {
+        printTableHeader();
+        for (Method method : uuidLongGenerator.getClass().getDeclaredMethods()) {
+            collisionAndNegativeCheck(method);
+        }
+    }
+
+    private void printTableHeader() {
+        logger.info(String.format("%-30s %-15s %-15s %-15s %-15s%n", "Approach", "collisions", "negatives", "collision", "negative"));
+        logger.info(String.format("%-30s %-15s %-15s %-15s %-15s%n", "(method name)", "count", "count", "probability", "probability"));
+        System.out.println("--------------------------------------------------------------------------------------------");
+    }
+
+    private void printOutput(String method, int collisionsCount, int negativeCount, double collisionsProbability, double negativeProbability) {
+        DecimalFormat decimalFormat = new DecimalFormat("#.#####");
+        logger.info(String.format("%-30s %-15s %-15s %-15s %-15s", method, collisionsCount, negativeCount, decimalFormat.format(collisionsProbability), decimalFormat.format(negativeProbability)));
+    }
+
+    private void collisionAndNegativeCheck(Method method) throws InvocationTargetException, IllegalAccessException {
+        Set<Long> uniqueValues = new HashSet<>();
+        int collisions = 0;
+        int negative = 0;
+
+        for (int i = 0; i < n; i++) {
+            long uniqueValue = (long) method.invoke(uuidLongGenerator);
+            if (!uniqueValues.add(uniqueValue)) {
+                collisions++;
+            }
+            if (uniqueValue < 0) {
+                negative++;
+            }
+        }
+
+        double collisionsProbability = (double) collisions / n;
+        double negativeProbability = (double) negative / n;
+        printOutput(method.getName(), collisions, negative, collisionsProbability, negativeProbability);
+
+        assertThat(collisionsProbability).isLessThan(COLLISION_THRESHOLD);
+    }
+}