Add JUnit tests for Parser class

src/test/java/duke/ParserTest.java

@@ -0,0 +1,31 @@
+package duke;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+public class ParserTest {
+
+    @Test
+    public void command_singleWordCommand_parsedCorrectly() {
+        Parser parser = new Parser("bye");
+        String result = parser.command();
+        assertEquals("bye", result);
+    }
+
+    @Test
+    public void commandOnly_singleWordCommand_returnsTrue() {
+        Parser parser = new Parser("bye");
+        assertTrue(parser.commandOnly());
+    }
+
+    @Test
+    public void commandOnly_multiWordCommand_returnsFalse() {
+        Parser parser = new Parser("todo read book");
+        assertFalse(parser.commandOnly());
+    }
+
+}
+
+