Update the README.md of testing about the steps to run the tests

Author: dianfu

testing/README.md

@@ -1 +1,76 @@
-It gives basic examples on how to write unit tests in external projects which depend on PyFlink.
+It gives a basic example on how to write unit tests in an external project which depends on PyFlink.
+
+You could execute the unit tests according to the following steps:
+- Create a Python virtual environment and install PyFlink
+```shell
+cd testing
+python3 -m venv .venv
+source .venv/bin/activate
+pip install .
+```
+
+- Check that PyFlink is installed successfully
+```shell
+python -c "import pyflink;import os;print(os.path.dirname(os.path.abspath(pyflink.__file__))+'/log')"
+```
+
+It will print something like the following: 
+```shell
+/Users/dianfu/code/src/github/pyflink-faq/testing/.venv/lib/python3.8/site-packages/pyflink/log
+```
+
+Execute the following command:
+```shell
+ls -lh /Users/dianfu/code/src/github/pyflink-faq/testing/.venv/lib/python3.8/site-packages/pyflink/
+```
+
+The structure should be as following:
+```
+total 136
+-rw-r--r--   1 dianfu  staff   1.3K Apr 25 09:26 README.txt
+-rw-r--r--   1 dianfu  staff   1.9K Apr 25 09:26 __init__.py
+drwxr-xr-x  11 dianfu  staff   352B Apr 25 09:26 __pycache__
+drwxr-xr-x  25 dianfu  staff   800B Apr 25 09:26 bin
+drwxr-xr-x  21 dianfu  staff   672B Apr 25 09:26 common
+drwxr-xr-x  13 dianfu  staff   416B Apr 25 09:26 conf
+drwxr-xr-x  20 dianfu  staff   640B Apr 25 09:26 datastream
+drwxr-xr-x   4 dianfu  staff   128B Apr 25 09:26 examples
+-rw-r--r--   1 dianfu  staff   3.2K Apr 25 09:26 find_flink_home.py
+drwxr-xr-x  25 dianfu  staff   800B Apr 25 09:26 fn_execution
+-rw-r--r--   1 dianfu  staff   9.1K Apr 25 09:26 gen_protos.py
+-rw-r--r--   1 dianfu  staff   7.6K Apr 25 09:26 java_gateway.py
+drwxr-xr-x  11 dianfu  staff   352B Apr 25 09:26 lib
+drwxr-xr-x  28 dianfu  staff   896B Apr 25 09:26 licenses
+drwxr-xr-x   4 dianfu  staff   128B Apr 25 09:26 log
+drwxr-xr-x   5 dianfu  staff   160B Apr 25 09:26 metrics
+drwxr-xr-x   4 dianfu  staff   128B Apr 25 09:26 opt
+drwxr-xr-x  11 dianfu  staff   352B Apr 25 09:26 plugins
+-rw-r--r--   1 dianfu  staff   1.3K Apr 25 09:26 pyflink_callback_server.py
+-rw-r--r--   1 dianfu  staff    12K Apr 25 09:26 pyflink_gateway_server.py
+-rw-r--r--   1 dianfu  staff   5.3K Apr 25 09:26 serializers.py
+-rw-r--r--   1 dianfu  staff   7.9K Apr 25 09:26 shell.py
+drwxr-xr-x  31 dianfu  staff   992B Apr 25 09:26 table
+drwxr-xr-x   6 dianfu  staff   192B Apr 25 09:26 util
+-rw-r--r--   1 dianfu  staff   1.1K Apr 25 09:26 version.py
+```
+Please checks that the directory `lib`, `opt`, `plugins` should be available.
+
+- Execute command `python3 -m unittest test_table_api.TableTests.test_scalar_function` to run the unit test
+
+You will see the following output, which means that the test has run successfully:
+```
+(.venv) (base) dianfu@B-7174MD6R-1908 testing % python3 -m unittest test_table_api.TableTests.test_scalar_function                            
+Using %s as FLINK_HOME... /Users/dianfu/code/src/github/pyflink-faq/testing/.venv/lib/python3.8/site-packages/pyflink
+Skipped download /Users/dianfu/code/src/github/pyflink-faq/testing/flink-python_2.11-1.14.4-tests.jar since it already exists.
+/Users/dianfu/miniconda3/lib/python3.8/subprocess.py:946: ResourceWarning: subprocess 71018 is still running
+  _warn("subprocess %s is still running" % self.pid,
+ResourceWarning: Enable tracemalloc to get the object allocation traceback
+Downloading jar org.apache.flink:flink-table-planner_2.11:1.14.4:jar:tests
+/Users/dianfu/code/src/github/pyflink-faq/testing/.venv/lib/python3.8/site-packages/pyflink/table/table_environment.py:538: DeprecationWarning: Deprecated in 1.10. Use create_table instead.
+  warnings.warn("Deprecated in 1.10. Use create_table instead.", DeprecationWarning)
+.
+----------------------------------------------------------------------
+Ran 1 test in 32.746s
+
+OK
+```