Add G-Counter (Grow-only Counter) (#4965)

src/test/java/com/thealgorithms/datastructures/crdt/GCounterTest.java

@@ -0,0 +1,54 @@
+package com.thealgorithms.datastructures.crdt;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+public class GCounterTest {
+    @Test
+    void increment() {
+        GCounter counter = new GCounter(0, 3);
+        counter.increment();
+        counter.increment();
+        counter.increment();
+        assertEquals(3, counter.value());
+    }
+
+    @Test
+    void merge() {
+        GCounter counter1 = new GCounter(0, 3);
+        counter1.increment();
+        GCounter counter2 = new GCounter(1, 3);
+        counter2.increment();
+        counter2.increment();
+        GCounter counter3 = new GCounter(2, 3);
+        counter3.increment();
+        counter3.increment();
+        counter3.increment();
+        counter1.merge(counter2);
+        counter1.merge(counter3);
+        counter2.merge(counter1);
+        counter3.merge(counter2);
+        assertEquals(6, counter1.value());
+        assertEquals(6, counter2.value());
+        assertEquals(6, counter3.value());
+    }
+
+    @Test
+    void compare() {
+        GCounter counter1 = new GCounter(0, 5);
+        GCounter counter2 = new GCounter(3, 5);
+        counter1.increment();
+        counter1.increment();
+        counter2.merge(counter1);
+        counter2.increment();
+        counter2.increment();
+        assertTrue(counter1.compare(counter2));
+        counter1.increment();
+        counter2.increment();
+        counter2.merge(counter1);
+        assertTrue(counter1.compare(counter2));
+        counter1.increment();
+        assertFalse(counter1.compare(counter2));
+    }
+}