diff --git a/bitcoin_trading_simulation.py b/bitcoin_trading_simulation.py
index cb07d20..8972e46 100644
--- a/bitcoin_trading_simulation.py
+++ b/bitcoin_trading_simulation.py
@@ -142,6 +142,19 @@ def countdown(quiet=False):
     if args.no_color:
         Colors.disable()
 
+    if args.days <= 0:
+        print(f"{Colors.FAIL}Error: --days must be a positive integer.{Colors.ENDC}")
+        sys.exit(1)
+    if args.initial_cash <= 0:
+        print(f"{Colors.FAIL}Error: --initial-cash must be positive.{Colors.ENDC}")
+        sys.exit(1)
+    if args.initial_price <= 0:
+        print(f"{Colors.FAIL}Error: --initial-price must be positive.{Colors.ENDC}")
+        sys.exit(1)
+    if args.volatility < 0:
+        print(f"{Colors.FAIL}Error: --volatility must be non-negative.{Colors.ENDC}")
+        sys.exit(1)
+
     # Simulate prices
     prices = simulate_bitcoin_prices(days=args.days, initial_price=args.initial_price, volatility=args.volatility)
 
diff --git a/test_cli.py b/test_cli.py
new file mode 100644
index 0000000..23eef17
--- /dev/null
+++ b/test_cli.py
@@ -0,0 +1,49 @@
+import subprocess
+import pytest
+import sys
+
+def run_cli(args):
+    """Runs the CLI script with given arguments."""
+    cmd = [sys.executable, "bitcoin_trading_simulation.py"] + args
+    result = subprocess.run(
+        cmd,
+        capture_output=True,
+        text=True
+    )
+    return result
+
+def test_cli_negative_days():
+    result = run_cli(["--days", "-5"])
+    assert result.returncode == 1
+    assert "Error: --days must be a positive integer." in result.stdout
+
+def test_cli_zero_days():
+    result = run_cli(["--days", "0"])
+    assert result.returncode == 1
+    assert "Error: --days must be a positive integer." in result.stdout
+
+def test_cli_negative_cash():
+    result = run_cli(["--initial-cash", "-100"])
+    assert result.returncode == 1
+    assert "Error: --initial-cash must be positive." in result.stdout
+
+def test_cli_zero_cash():
+    result = run_cli(["--initial-cash", "0"])
+    assert result.returncode == 1
+    assert "Error: --initial-cash must be positive." in result.stdout
+
+def test_cli_negative_price():
+    result = run_cli(["--initial-price", "-500"])
+    assert result.returncode == 1
+    assert "Error: --initial-price must be positive." in result.stdout
+
+def test_cli_negative_volatility():
+    result = run_cli(["--volatility", "-0.5"])
+    assert result.returncode == 1
+    assert "Error: --volatility must be non-negative." in result.stdout
+
+def test_cli_valid_run():
+    # Run with a short duration and quiet mode for speed
+    result = run_cli(["--days", "5", "--quiet", "--no-color"])
+    assert result.returncode == 0
+    assert "Final Portfolio Performance" in result.stdout