datasette.client internal requests mechanism

Closes #943

* Datasette now requires httpx>=0.15
* Support OPTIONS without 500, closes #1001
* Added internals tests for datasette.client methods
* Datasette's own test mechanism now uses httpx to simulate requests
* Tests simulate HTTP 1.1 now
* Added base_url in a bunch more places
* Mark some tests as xfail - will remove that when new httpx release ships: #1005

tests/test_internals_datasette_client.py

@@ -0,0 +1,44 @@
+from .fixtures import app_client
+import httpx
+import pytest
+
+
+@pytest.fixture
+def datasette(app_client):
+    return app_client.ds
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "method,path,expected_status",
+    [
+        ("get", "/", 200),
+        ("options", "/", 405),
+        ("head", "/", 200),
+        ("put", "/", 405),
+        ("patch", "/", 405),
+        ("delete", "/", 405),
+    ],
+)
+async def test_client_methods(datasette, method, path, expected_status):
+    client_method = getattr(datasette.client, method)
+    response = await client_method(path)
+    assert isinstance(response, httpx.Response)
+    assert response.status_code == expected_status
+    # Try that again using datasette.client.request
+    response2 = await datasette.client.request(method, path)
+    assert response2.status_code == expected_status
+
+
+@pytest.mark.asyncio
+async def test_client_post(datasette):
+    response = await datasette.client.post(
+        "/-/messages",
+        data={
+            "message": "A message",
+        },
+        allow_redirects=False,
+    )
+    assert isinstance(response, httpx.Response)
+    assert response.status_code == 302
+    assert "ds_messages" in response.cookies