Added optional tests for type stub adherence

Adds mypy dependencny to github tests

Author: ImFstAsFckBoi

.github/workflows/pr-tests.yml

@@ -36,6 +36,6 @@ jobs:
       run: |
         python3 -m venv .env # maturin requires a virtualenv
         source .env/bin/activate
-        pip3 install maturin pytest
+        pip3 install maturin pytest mypy
         maturin develop
         pytest

tests/test_suite.py

@@ -287,6 +287,33 @@ def test_int64(provider):
     res = cur.execute("SELECT * FROM data")
     assert [(1, 1099511627776)] == res.fetchall()
 
+def test_type_adherence(capsys):
+    try:
+        from mypy.stubtest import test_stubs, parse_options
+    except (ImportError, ModuleNotFoundError):
+        # skip test if mypy not installed
+        pytest.skip("Cant test type stubs without mypy installed")
+
+    # run mypy stubtest tool. Equivalent to running the following the terminal
+    """
+    stubtest --concise libsql_experimental | \
+        grep -v 'which is incompatible with stub argument type'
+    """
+    test_stubs(parse_options(["--concise", "libsql_experimental"]))
+    cap = capsys.readouterr()
+
+    # this is part of error reported if is default parameter is ellipsis
+    # `arg: type = ...` which is a nicer way to hide implementation from user
+    # than having the more "correct" `arg: type | None = None` everywhere
+    ellipsis_err = "which is incompatible with stub argument type"
+
+    lines = cap.out.split("\n")
+    lines = filter(lambda x: ellipsis_err not in x, lines)  # filter false positives from ellipsis
+    lines = filter(lambda x: len(x) != 0, lines)  # filter empty lines
+
+    # there will always be one error which i dont know how to get rid of
+    # `libsql_experimental.libsql_experimental failed to find stubs`
+    assert len(list(lines)) == 1
 
 def connect(provider, database, isolation_level="DEFERRED", autocommit=-1):
     if provider == "libsql-remote":