[Test proxy] Add migration guide (Azure#20469)

doc/dev/test_proxy_migration_guide.md

@@ -0,0 +1,176 @@
+# Guide for migrating to the test proxy from vcrpy
+
+This guide describes the changes that service SDKs should make to their test frameworks in order to take advantage of
+the Azure SDK test proxy.
+
+Documentation of the motivations and goals of the test proxy can be found [here][general_docs] in the azure-sdk-tools
+GitHub repository, and documentation of how to set up and use the proxy can be found [here][detailed_docs].
+
+## Update existing tests
+
+### Current test structure
+
+Test classes currently inherit from AzureTestCase, and test methods can optionally use decorators:
+
+```py
+from devtools_testutils import AzureTestCase
+
+class TestExample(AzureTestCase):
+
+    def test_example(self):
+        ...
+
+    @ExamplePreparer()
+    def test_example_with_preparer(self):
+        ...
+```
+
+### New test structure
+
+To use the proxy, test classes should inherit from AzureRecordedTestCase and recorded test methods should use a
+RecordedByProxy decorator:
+
+```py
+from devtools_testutils import AzureRecordedTestCase, RecordedByProxy
+
+class TestExample(AzureRecordedTestCase):
+
+    @RecordedByProxy
+    def test_example(self):
+        ...
+
+    @ExamplePreparer()
+    @RecordedByProxy
+    def test_example_with_preparer(self):
+        ...
+```
+
+For async tests, import the RecordedByProxyAsync decorator from `devtools_testutils.aio` and use it in the same
+way as RecordedByProxy.
+
+> **Note:** since AzureRecordedTestCase doesn't inherit from `unittest.TestCase`, test class names need to start
+> with "Test" in order to be properly collected by pytest by default. For more information, please refer to
+> [pytest's documentation][pytest_collection].
+
+## Run the tests
+
+### Perform one-time setup
+
+The test proxy is made available for your tests via a Docker container. Some tests require an SSL connection to work, so
+the Docker image used for the container has a certificate imported that you need to trust on your machine. Instructions
+on how to do so can be found [here][proxy_cert_docs].
+
+### Start the proxy server
+
+There is a [PowerShell script][docker_start_proxy] in `eng/common/testproxy` that will fetch the proxy Docker image if
+you don't already have it, and will start or stop a container running the image for you. You can run the following
+command from the root of the `azure-sdk-for-python` directory to start the container whenever you want to make the test
+proxy available for running tests:
+
+```powershell
+.\eng\common\testproxy\docker-start-proxy.ps1 "start"
+```
+
+Note that the proxy is available as long as the container is running. In other words, you don't need to start and
+stop the container for each test run or between tests for different SDKs. You can run the above command in the morning
+and just stop the container whenever you'd like. To stop the container, run the same command but with `"stop"` in place
+of `"start"`. In the future, the proxy container will be set up and started automatically when tests are run, and
+starting it manually will be optional.
+
+For more details on proxy startup, please refer to the [proxy documentation][detailed_docs].
+
+### Record or play back tests
+
+Configuring live and playback tests is done with the `AZURE_TEST_RUN_LIVE` environment variable. When this variable is
+set to "true" or "yes", live tests will run and produce recordings. When this variable is set to "false" or "no", or
+not set at all, tests will run in playback mode and attempt to match existing recordings.
+
+Recordings for a given package will end up in that package's `/tests/recordings` directory, just like they currently
+do.
+
+> **Note:** at this time, support for configuring live or playback tests with a `testsettings_local.cfg` file has been
+> deprecated in favor of using just `AZURE_TEST_RUN_LIVE`.
+
+### Register sanitizers
+
+Since the test proxy doesn't use [`vcrpy`][vcrpy], tests don't use a scrubber to sanitize values in recordings.
+Instead, sanitizers (as well as matchers and transforms) can be registered on the proxy as detailed in
+[this][sanitizers] section of the proxy documentation. At the time of writing, sanitizers can be registered via the
+`add_sanitizer` method in `devtools_testutils`.
+
+Sanitizers, matchers, and transforms remain registered until the proxy container is stopped, so for any sanitizers that
+are shared by different tests, using a session fixture declared in a `conftest.py` file is recommended. Please refer to
+[pytest's scoped fixture documentation][pytest_fixtures] for more details.
+
+For example, to sanitize URIs in recordings, you can set up a URI sanitizer for all tests in the pytest session by
+adding something like the following in the package's `conftest.py` file:
+
+```python
+from devtools_testutils import add_sanitizer
+
+@pytest.fixture(scope="session")
+def sanitize_uris():
+    add_sanitizer(ProxyRecordingSanitizer.URI, value="fakeendpoint")
+```
+
+`add_sanitizer` accepts a sanitizer, matcher, or transform type from the ProxyRecordingSanitizer enum as a required
+parameter. Keyword-only arguments can be provided to customize the sanitizer; for example, in the snippet above, any
+request URIs that match the default URI regular expression will have their domain name replaced with "fakeendpoint". A
+request made to `https://tableaccount.table.core.windows.net` will be recorded as being made to
+`https://fakeendpoint.table.core.windows.net`.
+
+## Implementation details
+
+### What does the test proxy do?
+
+The gist of the test proxy is that it stands in between your tests and the service. What this means is that test
+requests which would usually go straight to the service should instead point to the locally-hosted test proxy.
+
+For example, if an operation would typically make a GET request to
+`https://fakeazsdktestaccount.table.core.windows.net/Tables`, that operation should now be sent to
+`https://localhost:5001/Tables` instead. The original endpoint should be stored in an `x-recording-upstream-base-uri` --
+the proxy will send the original request and record the result.
+
+The RecordedByProxy and RecordedByProxyAsync decorators patch test requests to do this for you.
+
+### How does the test proxy know when and what to record or play back?
+
+This is achieved by making POST requests to the proxy server that say whether to start or stop recording or playing
+back, as well as what test is being run.
+
+To start recording a test, the server should be primed with a POST request:
+
+```
+URL: https://localhost:5001/record/start
+headers {
+    "x-recording-file": "<path-to-test>/recordings/<testfile>.<testname>"
+}
+```
+
+This will return a recording ID in an `x-recording-id` header. This ID should be sent as an `x-recording-id` header in
+all further requests during the test.
+
+After the test has finished, a POST request should be sent to indicate that recording is complete:
+
+```
+URL: https://localhost:5001/record/stop
+headers {
+    "x-recording-id": "<x-recording-id>"
+}
+```
+
+Running tests in playback follows the same pattern, except that requests will be sent to `/playback/start` and
+`/playback/stop` instead. A header, `x-recording-mode`, should be set to `record` for all requests when recording and
+`playback` when playing recordings back. More details can be found [here][detailed_docs].
+
+The RecordedByProxy and RecordedByProxyAsync decorators send the appropriate requests at the start and end of each test
+case.
+
+[detailed_docs]: https://github.com/Azure/azure-sdk-tools/tree/main/tools/test-proxy/Azure.Sdk.Tools.TestProxy/README.md
+[docker_start_proxy]: https://github.com/Azure/azure-sdk-for-python/blob/main/eng/common/testproxy/docker-start-proxy.ps1
+[general_docs]: https://github.com/Azure/azure-sdk-tools/blob/main/tools/test-proxy/README.md
+[proxy_cert_docs]: https://github.com/Azure/azure-sdk-tools/blob/main/tools/test-proxy/documentation/trusting-cert-per-language.md
+[pytest_collection]: https://docs.pytest.org/latest/goodpractices.html#test-discovery
+[pytest_fixtures]: https://docs.pytest.org/latest/fixture.html#scope-sharing-fixtures-across-classes-modules-packages-or-session
+[sanitizers]: https://github.com/Azure/azure-sdk-tools/blob/main/tools/test-proxy/Azure.Sdk.Tools.TestProxy/README.md#session-and-test-level-transforms-sanitiziers-and-matchers
+[vcrpy]: https://vcrpy.readthedocs.io

tools/azure-sdk-tools/devtools_testutils/proxy_testcase.py

@@ -24,6 +24,10 @@
 from .config import PROXY_URL
 
 
+# To learn about how to migrate SDK tests to the test proxy, please refer to the migration guide at
+# https://github.com/Azure/azure-sdk-for-python/blob/main/doc/dev/test_proxy_migration_guide.md
+
+
 # defaults
 RECORDING_START_URL = "{}/record/start".format(PROXY_URL)
 RECORDING_STOP_URL = "{}/record/stop".format(PROXY_URL)