Add py_test example.

BUILD.bazel

@@ -30,6 +30,20 @@ py_binary(
     python_version = "PY3",
 )
 
+py_test(
+    name = "main_test",
+    srcs = ["main_test.py"],
+    deps = [
+        requirement("attrs"),
+        requirement("more-itertools"),
+        requirement("packaging"),
+        requirement("pluggy"),
+        requirement("py"),
+        requirement("pytest"),
+        requirement("wcwidth"),
+    ],
+)
+
 ####################
 # Docker Image
 ####################

README.md

@@ -29,6 +29,12 @@ Host python version is 3.6.9
 Successfully imported psycopg2-binary!
 ```
 
+# py_test demo
+
+```
+bazel test //:main_test
+```
+
 # Docker Image Demo
 
 The image we're using is `python3:3.8.3-slim-buster`, which matches the python

main_test.py

@@ -0,0 +1,12 @@
+import platform
+import pytest
+import sys
+
+class TestPythonVersion:
+    def test_version(self):
+        assert('bazel-out/k8-fastbuild/bin/main_test.runfiles/python_interpreter/python_bin' in sys.executable)
+        assert(platform.python_version() == "3.8.3")
+
+if __name__ == "__main__":
+    import pytest
+    raise SystemExit(pytest.main([__file__]))

requirements.txt

@@ -1 +1,8 @@
+attrs==19.3.0
+more-itertools==8.2.0
+packaging==20.3
+pluggy==0.13.1
 psycopg2-binary==2.8.5
+py==1.8.1
+pytest==5.4.1
+wcwidth==0.1.9