Tidy LCS tests

Author: beauagainagainagainagainagain

dynamic_programming/tests/__init__.py

@@ -0,0 +1 @@
+"""Test suite for :mod:`dynamic_programming`."""

dynamic_programming/tests/test_longest_common_subsequence.py

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+"""Tests for :mod:`dynamic_programming.longest_common_subsequence`."""
+
+from __future__ import annotations
+
+from typing import cast
+
+import pytest
+
+from dynamic_programming.longest_common_subsequence import longest_common_subsequence
+
+
+def _is_subsequence(candidate: str, target: str) -> bool:
+    """Return ``True`` if ``candidate`` is a subsequence of ``target``."""
+    if not candidate:
+        return True
+
+    index = 0
+    for character in target:
+        if character == candidate[index]:
+            index += 1
+            if index == len(candidate):
+                return True
+    return index == len(candidate)
+
+
+@pytest.mark.parametrize(
+    ("first", "second", "expected_length", "expected_subsequence"),
+    [
+        ("programming", "gaming", 6, "gaming"),
+        ("physics", "smartphone", 2, "ph"),
+        ("computer", "food", 1, "o"),
+        ("abcdef", "ace", 3, "ace"),
+        ("ABCD", "ACBD", 3, "ABD"),
+    ],
+)
+def test_longest_common_subsequence_known_examples(
+    first: str, second: str, expected_length: int, expected_subsequence: str
+) -> None:
+    """The doctest examples continue to work when executed by ``pytest``."""
+    length, subsequence = longest_common_subsequence(first, second)
+    assert length == expected_length
+    assert subsequence == expected_subsequence
+
+
+@pytest.mark.parametrize(
+    ("first", "second"),
+    [
+        ("", "abc"),
+        ("abc", ""),
+        ("", ""),
+        ("abc", "def"),
+        ("a", "b"),
+    ],
+)
+def test_longest_common_subsequence_no_common_subsequence(
+    first: str, second: str
+) -> None:
+    """Pairs with no shared subsequence should return ``(0, "")``."""
+    length, subsequence = longest_common_subsequence(first, second)
+    assert length == 0
+    assert subsequence == ""
+
+
+def test_longest_common_subsequence_multiple_valid_answers() -> None:
+    """When many LCS strings exist, the chosen answer is still valid."""
+    first = "ABCBDAB"
+    second = "BDCABA"
+
+    length, subsequence = longest_common_subsequence(first, second)
+
+    assert length == 4
+    assert subsequence in {"BCAB", "BCBA", "BDAB"}
+    assert _is_subsequence(subsequence, first)
+    assert _is_subsequence(subsequence, second)
+
+
+def test_longest_common_subsequence_is_a_subsequence() -> None:
+    """The reported subsequence is present in both inputs and has the right length."""
+    first = "abracadabra"
+    second = "avada kedavra"
+
+    length_1, subsequence_1 = longest_common_subsequence(first, second)
+    length_2, subsequence_2 = longest_common_subsequence(second, first)
+
+    assert length_1 == length_2
+    assert len(subsequence_1) == length_1
+    assert len(subsequence_2) == length_2
+    assert _is_subsequence(subsequence_1, first)
+    assert _is_subsequence(subsequence_1, second)
+    assert _is_subsequence(subsequence_2, first)
+    assert _is_subsequence(subsequence_2, second)
+
+
+def test_longest_common_subsequence_rejects_none_arguments() -> None:
+    """Both parameters must be strings and not ``None``."""
+    with pytest.raises(AssertionError):
+        longest_common_subsequence(cast(str, None), "abc")
+    with pytest.raises(AssertionError):
+        longest_common_subsequence("abc", cast(str, None))