[formrecognizer] Adding custom forms perf test (Azure#16969)

* Adding custom forms perf test

* improve test to use labeled model

* add README

* update test name

* use async training client

* rename file

* fix test check

* update readme cmd instructions

* update readme

sdk/formrecognizer/azure-ai-formrecognizer/tests/perfstress_tests/README.md

@@ -0,0 +1,45 @@
+# Form Recognizer Performance Tests
+
+In order to run the performance tests, the `azure-devtools` package must be installed. This is done as part of the `dev_requirements` install.
+Start by creating a new virtual environment for your perf tests. This will need to be a Python 3 environment, preferably >=3.7.
+
+### Setup for test resources
+
+The following environment variables will need to be set for the tests to access the live resources:
+
+```
+FORMRECOGNIZER_TEST_ENDPOINT=<form recognizer service endpoint>
+FORMRECOGNIZER_TEST_API_KEY=<form recognizer API Key>
+FORMRECOGNIZER_TRAINING_DATA_CONTAINER_SAS_URL=<SAS url for container with training data>
+```
+
+### Setup for perf test runs
+
+```cmd
+(env) ~/azure-ai-formrecognizer> pip install -r dev_requirements.txt
+(env) ~/azure-ai-formrecognizer> pip install -e .
+```
+
+## Test commands
+
+Once `azure-devtools` is installed, you will have access to the `perfstress` command line tool, which will scan the current module for runable perf tests. Only a specific test can be run at a time (i.e. there is no "run all" feature).
+
+```cmd
+(env) ~/azure-ai-formrecognizer> cd tests/perfstress_tests/
+(env) ~/azure-ai-formrecognizer/tests/perfstress_tests> perfstress
+```
+Using the `perfstress` command alone will list the available perf tests found. 
+
+### Common perf command line options
+These options are available for all perf tests:
+- `--duration=10` Number of seconds to run as many operations (the "run" function) as possible. Default is 10.
+- `--iterations=1` Number of test iterations to run. Default is 1.
+- `--parallel=1` Number of tests to run in parallel. Default is 1.
+- `--warm-up=5` Number of seconds to spend warming up the connection before measuring begins. Default is 5.
+- `--sync` Whether to run the tests in sync or async. Default is False (async). This flag must be used for Storage legacy tests, which do not support async.
+- `--no-cleanup` Whether to keep newly created resources after test run. Default is False (resources will be deleted).
+
+## Example command
+```cmd
+(env) ~/azure-ai-formrecognizer/tests/perfstress_tests> perfstress RecognizeCustomForms
+```

sdk/formrecognizer/azure-ai-formrecognizer/tests/perfstress_tests/perf_custom_forms.py

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+# coding=utf-8
+# ------------------------------------
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+# ------------------------------------
+
+import os
+import pytest
+import functools
+from io import BytesIO
+from datetime import date, time
+from azure_devtools.perfstress_tests import PerfStressTest
+from azure.core.credentials import AzureKeyCredential
+from azure.ai.formrecognizer import FormRecognizerClient, FormContentType
+from azure.ai.formrecognizer.aio import FormRecognizerClient as AsyncFormRecognizerClient, FormTrainingClient as AsyncFormTrainingClient
+
+class RecognizeCustomForms(PerfStressTest):   
+
+    def __init__(self, arguments):
+        super().__init__(arguments)
+
+        with open(os.path.abspath(os.path.join(os.path.abspath(__file__), "..", "./../sample_forms/forms/Form_1.jpg")), "rb") as fd:
+            self.custom_form_jpg = fd.read()
+
+        # read test related env vars
+        self.formrecognizer_storage_container_sas_url = os.environ["FORMRECOGNIZER_TRAINING_DATA_CONTAINER_SAS_URL"]
+        formrecognizer_test_endpoint = os.environ["FORMRECOGNIZER_TEST_ENDPOINT"]
+        form_recognizer_account_key = os.environ["FORMRECOGNIZER_TEST_API_KEY"]
+
+        # assign the clients that will be used in the perf tests
+        self.service_client = FormRecognizerClient(formrecognizer_test_endpoint, AzureKeyCredential(form_recognizer_account_key))
+        self.async_service_client = AsyncFormRecognizerClient(formrecognizer_test_endpoint, AzureKeyCredential(form_recognizer_account_key))
+
+        # training client will be used for model training in set up
+        self.async_training_client = AsyncFormTrainingClient(formrecognizer_test_endpoint, AzureKeyCredential(form_recognizer_account_key))
+
+    async def global_setup(self):
+        """The global setup is run only once."""
+        poller = await self.async_training_client.begin_training(
+            self.formrecognizer_storage_container_sas_url, 
+            use_training_labels=True, 
+            model_name="labeled")
+        model = await poller.result()
+        self.model_id = model.model_id
+
+    async def global_cleanup(self):
+        """The global cleanup is run only once."""
+        await self.async_training_client.delete_model(self.model_id)
+
+    async def close(self):
+        """This is run after cleanup."""
+        await self.async_service_client.close()
+        self.service_client.close()
+        await self.async_training_client.close()
+        await super().close()
+
+    def run_sync(self):
+        """The synchronous perf test."""
+        poller = self.service_client.begin_recognize_custom_forms(
+            self.model_id, 
+            self.custom_form_jpg, 
+            content_type=FormContentType.IMAGE_JPEG)
+        result = poller.result()
+        assert result
+
+    async def run_async(self):
+        """The asynchronous perf test."""
+        poller = await self.async_service_client.begin_recognize_custom_forms(
+            self.model_id, 
+            self.custom_form_jpg,
+            content_type=FormContentType.IMAGE_JPEG)
+        result = await poller.result()
+        assert result