Don't use urljoin for prepending a forward slash to paths.

Fixes #273.

Previously, `Path` used `urljoin` to prepend a forward slash to the
path. But `urljoin` is broken for no good reason:

    >>> from urllib.parse import urljoin
    >>> urljoin("/", "oh//no")
    '/oh/no'

Fix this by just adding a "/" if it's not there, which is what this
was trying to do in the first place.

Author: lewiscollard

respx/patterns.py

@@ -24,7 +24,6 @@
     Union,
 )
 from unittest.mock import ANY
-from urllib.parse import urljoin
 
 import httpx
 
@@ -429,7 +428,11 @@ def clean(
                 else "".join(f"%{byte:02x}" for byte in char.encode("utf-8")).upper()
                 for char in value
             )
-            path = urljoin("/", path)  # Ensure leading slash
+            # Ensure a leading slash. Note we don't use urljoin because its
+            # behaviour with multiple slashes in the path is incorrect - see
+            # https://github.com/lundberg/respx/issues/273
+            if not path.startswith("/"):
+                path = f"/{path}"
             value = httpx.URL(path).path
         elif self.lookup is Lookup.REGEX and isinstance(value, str):
             value = re.compile(value)

tests/test_patterns.py

@@ -224,6 +224,9 @@ def test_path_pattern():
     path.base = Path("/foo/")
     assert path.strip_base("/foo/bar/") == "/bar/"
 
+    # Regression test for https://github.com/lundberg/respx/issues/273
+    assert Path("foo//bar").clean("foo//bar") == "/foo//bar"
+
 
 @pytest.mark.parametrize(
     ("lookup", "params", "url", "expected"),