1 files changed, 77 insertions, 0 deletions
diff --git a/tests/library/algebra.test.py b/tests/library/algebra.test.py
new file mode 100644
index 0000000..ee4005d
--- /dev/null
+++ b/tests/library/algebra.test.py
@@ -0,0 +1,77 @@
+"""Chain <-> operator-algebra equivalence: ``+``, ``|`` and ``.use()`` emit the fluent-chain regex.
+
+Every character-class module constant is driven through both surfaces and the two
+emitted regex strings are asserted identical, so the operator algebra can never
+drift from the fluent builder it stands in for.
+"""
+
+import pytest
+
+from edify import (
+    ALPHANUMERIC,
+    ANY_CHAR,
+    CARRIAGE_RETURN,
+    DIGIT,
+    LETTER,
+    LOWERCASE,
+    NEW_LINE,
+    NON_DIGIT,
+    NON_WHITESPACE,
+    NON_WORD,
+    NULL_BYTE,
+    TAB,
+    UPPERCASE,
+    WHITESPACE,
+    WORD,
+    Pattern,
+)
+
+_CONSTANTS: dict[str, Pattern] = {
+    "ANY_CHAR": ANY_CHAR,
+    "WHITESPACE": WHITESPACE,
+    "NON_WHITESPACE": NON_WHITESPACE,
+    "DIGIT": DIGIT,
+    "NON_DIGIT": NON_DIGIT,
+    "WORD": WORD,
+    "NON_WORD": NON_WORD,
+    "NEW_LINE": NEW_LINE,
+    "CARRIAGE_RETURN": CARRIAGE_RETURN,
+    "TAB": TAB,
+    "NULL_BYTE": NULL_BYTE,
+    "LETTER": LETTER,
+    "UPPERCASE": UPPERCASE,
+    "LOWERCASE": LOWERCASE,
+    "ALPHANUMERIC": ALPHANUMERIC,
+}
+_IDS = list(_CONSTANTS)
+_VALUES = list(_CONSTANTS.values())
+
+
+[email protected]("constant", _VALUES, ids=_IDS)
+def test_plus_matches_chain_subexpression(constant: Pattern):
+    operator_form = (constant + DIGIT).to_regex_string()
+    chain_form = Pattern().subexpression(constant).subexpression(DIGIT).to_regex_string()
+    assert operator_form == chain_form
+
+
+[email protected]("constant", _VALUES, ids=_IDS)
+def test_or_matches_chain_any_of(constant: Pattern):
+    operator_form = (constant | DIGIT).to_regex_string()
+    chain_form = (
+        Pattern().any_of().subexpression(constant).subexpression(DIGIT).end().to_regex_string()
+    )
+    assert operator_form == chain_form
+
+
+[email protected]("constant", _VALUES, ids=_IDS)
+def test_use_matches_chain_subexpression(constant: Pattern):
+    use_form = Pattern().use(constant).to_regex_string()
+    chain_form = Pattern().subexpression(constant).to_regex_string()
+    assert use_form == chain_form
+
+
+[email protected]("constant", _VALUES, ids=_IDS)
+def test_operator_and_chain_compile_to_the_same_matcher(constant: Pattern):
+    operator_compiled = (constant + DIGIT).to_regex().source
+    chain_compiled = Pattern().subexpression(constant).subexpression(DIGIT).to_regex().source
+    assert operator_compiled == chain_compiled