add unit test

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

@@ -0,0 +1,63 @@
+package com.baeldung.uuid;
+
+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 java.util.concurrent.atomic.AtomicInteger;
+import java.util.stream.IntStream;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class UUIDLongGeneratorUnitTest {
+    final static int n = 1000000;
+    UUIDLongGenerator uuidLongGenerator = new UUIDLongGenerator();
+
+    @Test
+    void whenForeachGenerateLongValue_thenCollisionsCheck() {
+        printTableHeader();
+        for (Method method : uuidLongGenerator.getClass().getDeclaredMethods()) {
+            collisionAndNegativeCheck(method);
+        }
+    }
+
+    private void printTableHeader() {
+        System.out.format("%-30s %-15s %-15s %-15s %-15s%n", "Approach", "collisions", "negatives", "collision", "negative");
+        System.out.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("#.#####");
+        System.out.format("%-30s %-15s %-15s %-15s %-15s%n", method, collisionsCount, negativeCount, decimalFormat.format(collisionsProbability), decimalFormat.format(negativeProbability));
+    }
+
+    private void collisionAndNegativeCheck(Method method) {
+        Set<Long> uniqueValues = new HashSet<>();
+        AtomicInteger collisions = new AtomicInteger(0);
+        AtomicInteger negative = new AtomicInteger(0);
+
+        IntStream.range(0, n).forEach(i -> {
+            try {
+                long uniqueValue = (long) method.invoke(uuidLongGenerator);
+                if (!uniqueValues.add(uniqueValue)) {
+                    collisions.incrementAndGet();
+                }
+                if (uniqueValue < 0) {
+                    negative.incrementAndGet();
+                }
+            } catch (IllegalAccessException | InvocationTargetException e) {
+                throw new RuntimeException(e);
+            }
+        });
+
+        double collisionsProbability = (double) collisions.get() / n;
+        double negativeProbability = (double) negative.get() / n;
+        printOutput(method.getName(), collisions.get(), negative.get(), collisionsProbability, negativeProbability);
+
+        assertTrue(collisionsProbability <= 0.001); // threshold = 0.001
+    }
+}