Add regression tests

test/unit/regression/test_unstable_digest.py

@@ -0,0 +1,42 @@
+"""
+This module contains regression tests regarding the issue of unstable return values from the `digest` function.
+The tests ensure that the `digest` function consistently returns the expected output for given inputs.
+For more context and a detailed discussion of the problem, refer to the GitHub issue:
+https://github.com/Nicoretti/crc/issues/151
+"""
+
+import itertools
+
+import pytest
+
+import crc
+
+
+def test_original_regression():
+    reg = crc.Register(crc.Crc8.BLUETOOTH)
+    reg.init()
+    reg.update(b"Hello World!")
+
+    times = 10
+    expected = [81 for _ in range(0, times)]
+    actual = [reg.digest() for _ in range(0, times)]
+
+    assert actual == expected
+
+
+@pytest.mark.parametrize(
+    "configuration,times,expected",
+    [
+        (config, 10, crc.Calculator(config).checksum(b"Hello World!"))
+        for config in itertools.chain(crc.Crc8, crc.Crc16, crc.Crc32, crc.Crc64)
+    ],
+)
+def test_digest_is_stable(configuration, times, expected):
+    expected = [expected for _ in range(times)]
+
+    reg = crc.Register(configuration)
+    reg.init()
+    reg.update(b"Hello World!")
+    actual = [reg.digest() for _ in range(times)]
+
+    assert actual == expected