Enforce consistency in imports as part of build

This copies the config we use in the admin app, with a few changes
as discussed in the PR [1]. We'll apply these to our other apps.

[1]: https://github.com/alphagov/notifications-api/pull/3175#issuecomment-795530323

requirements_for_test.txt

@@ -1,6 +1,7 @@
 -r requirements.txt
 flake8==3.8.4
 flake8-bugbear==20.11.1
+isort==5.7.0
 moto==1.3.16
 pytest==6.1.2
 pytest-env==0.6.2

scripts/run_tests.sh

@@ -30,6 +30,9 @@ display_result $? 1 "Requirements check"
 flake8 .
 display_result $? 1 "Code style check"
 
+isort --check-only ./app ./tests
+display_result $? 2 "Import order check"
+
 # run with four concurrent threads
 py.test -n4 -v --maxfail=10
 display_result $? 2 "Unit tests"

setup.cfg

@@ -7,3 +7,13 @@ exclude = venv*,__pycache__,node_modules,cache,migrations,build,sample_cap_xml_d
 max-line-length = 120
 # W504 line break after binary operator
 extend_ignore=B306, W504
+
+
+[isort]
+line_length=80
+indent='    '
+multi_line_output=3
+known_third_party=notifications_utils,notifications_python_client
+known_first_party=app,tests
+include_trailing_comma=True
+use_parentheses=True