Add tests for A5KeyStreamGenerator.java, improve documentation (#5595)

src/test/java/com/thealgorithms/ciphers/a5/A5KeyStreamGeneratorTest.java

@@ -0,0 +1,60 @@
+package com.thealgorithms.ciphers.a5;
+
+import static com.thealgorithms.ciphers.a5.A5KeyStreamGenerator.FRAME_COUNTER_LENGTH;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import java.util.BitSet;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class A5KeyStreamGeneratorTest {
+
+    private A5KeyStreamGenerator keyStreamGenerator;
+    private BitSet sessionKey;
+    private BitSet frameCounter;
+
+    @BeforeEach
+    void setUp() {
+        keyStreamGenerator = new A5KeyStreamGenerator();
+
+        // Initialize session key and frame counter for testing
+        sessionKey = BitSet.valueOf(new long[] {0b1010101010101010L}); // Example 16-bit key
+        frameCounter = BitSet.valueOf(new long[] {0b0000000000000001L}); // Example 16-bit frame counter
+        keyStreamGenerator.initialize(sessionKey, frameCounter);
+    }
+
+    @Test
+    void testInitialization() {
+        // Verify that the internal state is set up correctly
+        assertNotNull(keyStreamGenerator, "KeyStreamGenerator should be initialized");
+    }
+
+    @Test
+    void testIncrementFrameCounter() {
+        // Generate key stream to increment the frame counter
+        keyStreamGenerator.getNextKeyStream();
+
+        // The frame counter should have been incremented
+        BitSet incrementedFrameCounter = keyStreamGenerator.getFrameCounter();
+
+        // Check if the incremented frame counter is expected
+        BitSet expectedFrameCounter = (BitSet) frameCounter.clone();
+        Utils.increment(expectedFrameCounter, FRAME_COUNTER_LENGTH);
+
+        assertEquals(expectedFrameCounter, incrementedFrameCounter, "Frame counter should be incremented after generating key stream");
+    }
+
+    @Test
+    void testGetNextKeyStreamProducesDifferentOutputs() {
+        // Generate a key stream
+        BitSet firstKeyStream = keyStreamGenerator.getNextKeyStream();
+
+        // Generate another key stream
+        BitSet secondKeyStream = keyStreamGenerator.getNextKeyStream();
+
+        // Assert that consecutive key streams are different
+        assertNotEquals(firstKeyStream, secondKeyStream, "Consecutive key streams should be different");
+    }
+}