Get the Damm module tested

projects/damm/BUILD

@@ -1,20 +1,6 @@
-py_library(
+py_project(
     name = "damm",
-    srcs = [
+    test_deps = [
-        "damm.py",
+        py_requirement("hypothesis"),
     ],
-    imports = [
-        "."
-    ],
-    visibility = [
-        "//visibility:public",
-    ]
-)
-
-py_pytest(
-    name = "test_damm",
-    srcs = glob(["test_*.py"]),
-    deps = [
-        ":damm",
-    ]
 )

projects/damm/src/python/damm.py

@@ -45,12 +45,20 @@ class Damm(NamedTuple):
         return f"{self.__class__.__name__}({self.value}, {self.encode(self.value)})"
 
     @classmethod
-    def encode(cls, value):
+    def checkdigit(cls, value: int) -> int:
+        """Compute a check digit for a given value."""
+
         state = 0
         for digit in str(value):
             state = cls.MATRIX[state][int(digit)]
         return state
 
+    @classmethod
+    def encode(cls, value: int) -> str:
+        """'encode' a value with a check digit."""
+
+        return f"{value}-{cls.checkdigit(value)}"
+
     @classmethod
     def verify(cls, value: str) -> bool:
         """Verify a Damm encoded number, returning its value if valid.
@@ -59,11 +67,13 @@ class Damm(NamedTuple):
         the string is correctly Damm encoded, the Damm of the entire string will be 0.
 
         """
-        return cls.encode(int(value.replace("-", ""))) == 0
+
+        return cls.checkdigit(int(value.replace("-", ""))) == 0
 
     @classmethod
     def from_str(cls, value: str) -> "Damm":
         """Verify a Damm coded string, and return its decoding."""
+
         if match := re.fullmatch(cls.DAMM_PATTERN, value):
             given_value = match.group("value")
             computed_code = cls.encode(given_value)

projects/damm/test/python/test_damm.py

@@ -0,0 +1,15 @@
+from damm import Damm
+
+import pytest
+
+
+@pytest.mark.parametrize('num', [
+    "0",    # 0 itself is the start Damm state
+    "37",   # [0, 3] => 7
+    "92",   # [0, 9] => 2
+    "1234", # Amusingly, this is a 0-product.
+])
+def test_num_verifies(num):
+    """Assert that known-good Damm checks pass."""
+
+    assert Damm.verify(num)

projects/damm/test/python/test_hypothesis.py

@@ -0,0 +1,11 @@
+from damm import Damm
+
+from hypothesis import given
+from hypothesis.strategies import integers
+
+
+@given(integers(0, 1<<512))
+def test_num_checks_verify(num):
+    """Assert the generated Damm check for number verifies."""
+
+    assert Damm.verify(Damm.encode(num))

projects/damm/test_damm.py

@@ -1,5 +0,0 @@
-"""
-
-"""
-
-from damm import Damm