Add test cases for CommandHistory

src/test/java/seedu/address/ui/CommandHistoryTest.java

@@ -0,0 +1,105 @@
+package seedu.address.ui;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import seedu.address.ui.util.CommandHistory;
+
+/**
+ * Unit tests for {@code CommandHistory}.
+ */
+public class CommandHistoryTest {
+
+    private CommandHistory commandHistory;
+
+    @BeforeEach
+    public void setUp() {
+        commandHistory = new CommandHistory();
+    }
+
+    @Test
+    public void addCommand_singleCommand_success() {
+        commandHistory.addCommand("first command");
+        assertEquals("first command", commandHistory.getPreviousCommand());
+    }
+
+    @Test
+    public void addCommand_multipleCommands_success() {
+        commandHistory.addCommand("first command");
+        commandHistory.addCommand("second command");
+        commandHistory.addCommand("third command");
+
+        assertEquals("third command", commandHistory.getPreviousCommand());
+        assertEquals("second command", commandHistory.getPreviousCommand());
+        assertEquals("first command", commandHistory.getPreviousCommand());
+    }
+
+    @Test
+    public void getPreviousCommand_noHistory_returnsNull() {
+        assertNull(commandHistory.getPreviousCommand());
+    }
+
+    @Test
+    public void getPreviousCommand_atStartOfHistory_returnsNull() {
+        commandHistory.addCommand("first command");
+
+        // Move to the start of the history
+        commandHistory.getPreviousCommand();
+        assertNull(commandHistory.getPreviousCommand());
+    }
+
+    @Test
+    public void getNextCommand_noHistory_returnsNull() {
+        assertNull(commandHistory.getNextCommand());
+    }
+
+    @Test
+    public void getNextCommand_atEndOfHistory_returnsNull() {
+        commandHistory.addCommand("first command");
+        commandHistory.addCommand("second command");
+
+        // Move to the start of history
+        commandHistory.getPreviousCommand();
+        commandHistory.getPreviousCommand();
+
+        // Move forward to the end of history
+        commandHistory.getNextCommand();
+        commandHistory.getNextCommand();
+        assertNull(commandHistory.getNextCommand());
+    }
+
+    @Test
+    public void getNextCommand_fromMiddleOfHistory_success() {
+        commandHistory.addCommand("first command");
+        commandHistory.addCommand("second command");
+        commandHistory.addCommand("third command");
+
+        // Move to the start of history
+        commandHistory.getPreviousCommand();
+        commandHistory.getPreviousCommand();
+        commandHistory.getPreviousCommand();
+
+        // Move forward one step in history
+        assertEquals("second command", commandHistory.getNextCommand());
+    }
+
+    @Test
+    public void addCommand_afterNavigatingHistory_resetsHistoryIndex() {
+        commandHistory.addCommand("first command");
+        commandHistory.addCommand("second command");
+
+        // Move to the start of history
+        commandHistory.getPreviousCommand();
+        commandHistory.getPreviousCommand();
+
+        // Add a new command
+        commandHistory.addCommand("new command");
+
+        // New command should be at the end of history
+        assertEquals("new command", commandHistory.getPreviousCommand());
+        assertNull(commandHistory.getNextCommand()); // At the end of history
+    }
+}