Add a 'remote' factor to enable remote data

tox.ini

@@ -1,8 +1,8 @@
 [tox]
 envlist =
-    py{37,38,39}-test{,-alldeps,-devdeps}{,-cov}
-    py{37,38,39}-test-numpy{117,118,119}
-    py{37,38,39}-test-astropy{lts,41,42}
+    py{37,38,39}-test{,-alldeps,-devdeps}{,-cov}{,-remote}
+    py{37,38,39}-test-numpy{117,118,119}{,-remote}
+    py{37,38,39}-test-astropy{lts,41,42}{,-remote}
     build_docs
     linkcheck
     codestyle
@@ -15,7 +15,9 @@ indexserver =
 
 [testenv]
 # Suppress display of matplotlib plots generated during docs build
-setenv = MPLBACKEND=agg
+setenv = 
+	MPLBACKEND=agg
+	remote: PYTEST_REMOTE_DATA=any
 
 # Pass through the following environment variables which may be needed for the CI
 passenv = HOME, WINDIR, LC_ALL, LC_CTYPE, CC, CI, TRAVIS
@@ -38,6 +40,7 @@ description =
     devdeps: with the latest developer version of key dependencies
     oldestdeps: with the oldest supported version of key dependencies
     cov: and test coverage
+    remote: with remote data
     numpy116: with numpy 1.16.*
     numpy117: with numpy 1.17.*
     numpy118: with numpy 1.18.*
@@ -72,8 +75,8 @@ extras =
 
 commands =
     pip freeze
-    !cov: pytest --pyargs astroplan {toxinidir}/docs {posargs}
-    cov: pytest --pyargs astroplan {toxinidir}/docs --cov astroplan --cov-config={toxinidir}/setup.cfg {posargs}
+    !cov: pytest --remote-data={env:PYTEST_REMOTE_DATA:none} --pyargs astroplan {toxinidir}/docs {posargs}
+    cov: pytest --remote-data={env:PYTEST_REMOTE_DATA:none} --pyargs astroplan {toxinidir}/docs --cov astroplan --cov-config={toxinidir}/setup.cfg {posargs}
     cov: coverage xml -o {toxinidir}/coverage.xml
 
 [testenv:build_docs]