[ AIRFLOW-4554] Test for sudo command, add some other test docs (apac…

…he#5310)

* AIRFLOW-4554 Unit tests use sudo conditionally

CONTRIBUTING.md

@@ -127,9 +127,12 @@ There are three ways to setup an Apache Airflow development environment.
   # Start docker in your Airflow directory
   docker run -t -i -v `pwd`:/airflow/ -w /airflow/ python:3 bash
 
-  # Install Airflow with all the required dependencies,
-  # including the devel which will provide the development tools
-  pip install -e '.[hdfs,hive,druid,devel]'
+  # To install all of airflows dependencies to run all tests (this is a lot)
+  pip install -e .
+  
+  # To run only certain tests install the devel requirements and whatever is required
+  # for your test.  See setup.py for the possible requirements. For example:
+  pip install -e '.[gcp,devel]'
 
   # Init the database
   airflow initdb
@@ -190,6 +193,10 @@ or a single test method:
 ```
 ./run_unit_tests.sh tests.core:CoreTest.test_check_operators -s --logging-level=DEBUG
 ```
+or another example:
+```
+./run_unit_tests.sh tests.contrib.operators.test_dataproc_operator:DataprocClusterCreateOperatorTest.test_create_cluster_deletes_error_cluster  -s --logging-level=DEBUG
+```
 
 To run the whole test suite with Docker Compose, do:
 

run_unit_tests.sh

@@ -61,8 +61,13 @@ if [ -f "${AIRFLOW_DB}" ]; then
 fi
 
 # For impersonation tests on Travis, make airflow accessible to other users via the global PATH
-# (which contains /usr/local/bin)
-sudo ln -sf "${VIRTUAL_ENV}/bin/airflow" /usr/local/bin/
+# (which contains /usr/local/bin).  Some test environments, like the docker instructions, won't have sudo and
+# are probably running as root anyway
+if command -v sudo > /dev/null; then
+  sudo ln -sf "${VIRTUAL_ENV}/bin/airflow" /usr/local/bin/
+else
+  ln -sf "${VIRTUAL_ENV}/bin/airflow" /usr/local/bin/
+fi
 
 echo "Starting the unit tests with the following nose arguments: "$nose_args
 nosetests $nose_args