Revise lazy wheel and its tests

src/pip/_internal/network/lazy_wheel.py

@@ -1,6 +1,6 @@
 """Lazy ZIP over HTTP"""
 
-__all__ = ['dist_from_wheel_url']
+__all__ = ['HTTPRangeRequestUnsupported', 'dist_from_wheel_url']
 
 from bisect import bisect_left, bisect_right
 from contextlib import contextmanager
@@ -23,13 +23,18 @@
     from pip._internal.network.session import PipSession
 
 
+class HTTPRangeRequestUnsupported(Exception):
+    pass
+
+
 def dist_from_wheel_url(name, url, session):
     # type: (str, str, PipSession) -> Distribution
     """Return a pkg_resources.Distribution from the given wheel URL.
 
     This uses HTTP range requests to only fetch the potion of the wheel
     containing metadata, just enough for the object to be constructed.
-    If such requests are not supported, RuntimeError is raised.
+    If such requests are not supported, HTTPRangeRequestUnsupported
+    is raised.
     """
     with LazyZipOverHTTP(url, session) as wheel:
         # For read-only ZIP files, ZipFile only needs methods read,
@@ -45,7 +50,8 @@ class LazyZipOverHTTP(object):
 
     This uses HTTP range requests to lazily fetch the file's content,
     which is supposed to be fed to ZipFile.  If such requests are not
-    supported by the server, raise RuntimeError during initialization.
+    supported by the server, raise HTTPRangeRequestUnsupported
+    during initialization.
     """
 
     def __init__(self, url, session, chunk_size=CONTENT_CHUNK_SIZE):
@@ -60,7 +66,7 @@ def __init__(self, url, session, chunk_size=CONTENT_CHUNK_SIZE):
         self._left = []  # type: List[int]
         self._right = []  # type: List[int]
         if 'bytes' not in head.headers.get('Accept-Ranges', 'none'):
-            raise RuntimeError('range request is not supported')
+            raise HTTPRangeRequestUnsupported('range request is not supported')
         self._check_zip()
 
     @property

tests/unit/test_network_lazy_wheel.py

@@ -3,9 +3,12 @@
 from pip._vendor.pkg_resources import Requirement
 from pytest import fixture, mark, raises
 
-from pip._internal.network.lazy_wheel import dist_from_wheel_url
+from pip._internal.network.lazy_wheel import (
+    HTTPRangeRequestUnsupported,
+    dist_from_wheel_url,
+)
 from pip._internal.network.session import PipSession
-from tests.lib.requests_mocks import MockResponse
+from tests.lib.server import file_response
 
 MYPY_0_782_WHL = (
     'https://files.pythonhosted.org/packages/9d/65/'
@@ -25,6 +28,16 @@ def session():
     return PipSession()
 
 
+@fixture
+def mypy_whl_no_range(mock_server, shared_data):
+    mypy_whl = shared_data.packages / 'mypy-0.782-py3-none-any.whl'
+    mock_server.set_responses([file_response(mypy_whl)])
+    mock_server.start()
+    base_address = 'http://{}:{}'.format(mock_server.host, mock_server.port)
+    yield "{}/{}".format(base_address, 'mypy-0.782-py3-none-any.whl')
+    mock_server.stop()
+
+
 @mark.network
 def test_dist_from_wheel_url(session):
     """Test if the acquired distribution contain correct information."""
@@ -35,12 +48,10 @@ def test_dist_from_wheel_url(session):
     assert set(dist.requires(dist.extras)) == MYPY_0_782_REQS
 
 
-@mark.network
-def test_dist_from_wheel_url_no_range(session, monkeypatch):
+def test_dist_from_wheel_url_no_range(session, mypy_whl_no_range):
     """Test handling when HTTP range requests are not supported."""
-    monkeypatch.setattr(session, 'head', lambda *a, **kw: MockResponse(b''))
-    with raises(RuntimeError):
-        dist_from_wheel_url('mypy', MYPY_0_782_WHL, session)
+    with raises(HTTPRangeRequestUnsupported):
+        dist_from_wheel_url('mypy', mypy_whl_no_range, session)
 
 
 @mark.network