Add an "invoke formatters" command

Author: abrookins

CONTRIBUTING.md

@@ -81,6 +81,12 @@ using `invoke standalone-tests`; similarly, RedisCluster tests can be run by usi
 Each run of tests starts and stops the various dockers required. Sometimes
 things get stuck, an `invoke clean` can help.
 
+## Linting and Formatting
+
+Call `invoke linters` to run linters without also running tests. This command will
+only report issues, not fix them automatically. Run `invoke formatters` to
+automatically format your code.
+
 ## Documentation
 
 If relevant, update the code documentation, via docstrings, or in `/docs`.

tasks.py

@@ -33,6 +33,12 @@ def linters(c):
     run("vulture redis whitelist.py --min-confidence 80")
     run("flynt --fail-on-change --dry-run tests redis")
 
+@task
+def formatters(c):
+    """Format code"""
+    run("black --target-version py37 tests redis")
+    run("isort tests redis")
+
 
 @task
 def all_tests(c):