diff --git a/tests/test_jit_decorator.py b/tests/test_jit_decorator.py
new file mode 100644
index 0000000..8e43449
--- /dev/null
+++ b/tests/test_jit_decorator.py
@@ -0,0 +1,67 @@
+import copapy as cp
+
+@cp.jit
+def calculation(x: float, y: float) -> float:
+    return sum(x ** 2 + y ** 2 + i for i in range(10))
+
+
+MASK = (1 << 31) - 1  # 0x7FFFFFFF
+
+
+def rotl31(x: int, r: int) -> int:
+    r %= 31
+    return ((x << r) | (x >> (31 - r))) & MASK
+
+
+def slow_31bit_int_list_hash(data: list[int], rounds: int = 5)-> int:
+    """
+    Intentionally slow hash using only 31-bit integer operations.
+    Input:  list[int]
+    Output: 31-bit integer
+    """
+
+    # 31-bit initial state (non-zero)
+    state = 0x1234567 & MASK
+
+    # Normalize input into 31-bit space
+    data = [abs(x) & MASK for x in data]
+
+    for r in range(rounds):
+        for i, x in enumerate(data):
+            # Mix index, round, and data
+            state ^= (x + i + r) & MASK
+
+            # Nonlinear mixing (carefully kept 31-bit)
+            state = (state * 1103515245) & MASK
+            state ^= (state >> 13)
+            state = (state * 12345) & MASK
+
+            # Data-dependent rotation (forces serial dependency)
+            rot = (x ^ state) % 31
+            state = rotl31(state, rot)
+
+        # Cross-round diffusion
+        state ^= (state >> 11)
+        state = (state * 1664525) & MASK
+        state ^= (state >> 17)
+
+    return state
+
+
+def test_decorator():
+    sumv = 0
+    y = 5.7
+    for i in range(2000):
+        x = i * 2.5
+        sumv = calculation(x, y) + sumv
+
+    assert abs(sumv - 166542418649.28778) < 1e14, sumv
+
+def test_hash():
+    nums = [12, 99, 2024]
+    h_ref = slow_31bit_int_list_hash(nums)
+    print(h_ref)
+
+    h = cp.jit(slow_31bit_int_list_hash)(nums)
+    print(h)
+    assert h == h_ref