Support dev only and sync

[sssoleileraaa]

Description

Closes #153

See test plan: freedomofpress/securedrop-log#24

[kushaldas]

Note: The dev-requirements.txt file gets an update in the relatest tests here as importlib-metadata has an update.

Test new venv target:

1. Create a dev env
   • make venv && source .venv/bin/activate creates dev env with all dev deps installed

Test updating existing requirements.txt file

1. Run make requirements
   • Verify that you see no local changes since the dependency specification is already met (redis==3.3.11)
2. Update dependency specification to redis>=3.3.11 and run make requirements
   • Verify that you see no local changes since the dependency specification is already met (3.3.11 is >= 3.3.11)
3. Add a new dependency spec: zipp<3 to requirements.in and run make requirements
   • Verify that you see the new dependency pinned in requirements.txt
   • NEW SYNC BEHAVIOR Verify that you see the existing previously dev-only dependency downgraded in dev-requirements.txt to match what's in prod

Test creating new requirements.txt file

1. Make sure to undo chnages from previous test
2. rm -r requirements/requirements.txt
3. make requirements
   • Verify that you see no local changes since the only dependency specification is redis==3.3.11 which matches what we have on remote
4. rm -r requirements/requirements.txt
5. Update dependency specification to redis>=3.3.11 and run make requirements
   • Verify that you see the latest version of redis pinned in requirements.txt
   • NEW SYNC BEHAVIOR Verify that you see the same version of redis in dev-requirements.txt to match what's in prod

Test updating a single dependency

1. Update dependency specification to redis>=3.3.11,<3.5 and run PACKAGE=redis make update-dependency
   • Verify that you see version 3.4.1 of redis pinned in requirements.txt
   • NEW SYNC BEHAVIOR Verify that you see the same version of redis in dev-requirements.txt to match what's in prod
2. Try to add a new dependency that doesn't exist in requirements.in by running PACKAGE=pytest make update-dependency
   • Verify that you see no local changes

Test updating all dev-only dependencies

1. make update-dev-only-dependencies
   • Verify that you see no local changes since the only dev dependency is already the latest
2. Add six<1 and redis (with no ==, <=, or >=) to dev-requirements.in and run make update-dev-only-dependencies
   • Verify that redis is still pinned to the same version as prod
   • Verify six==0.9.2 is pinned in dev-requirements.txt
3. Update six<1 to just six and run make update-dev-only-dependencies
   • Verify latest version of six is pinned in dev-requirements.txt