Switch repository used to test sub-directory support

Using a repository that contains invlid instructions in the root of the
repository so that the test for subdirectory support will fail if
repo2docker doesn't actually switch into the requested sub-directory.

repo2docker/app.py

@@ -704,9 +704,10 @@ class Repo2Docker(Application):
             self.fetch(self.repo, self.ref, checkout_path)
 
             if self.subdir:
-                checkout_path = os.path.join(checkout_path, self.subdir).rstrip('/')
-                if not os.path.exists(checkout_path):
-                    self.log.error('Subdirectory %s does not exist', self.subdir, extra=dict(phase='failure'))
+                checkout_path = os.path.join(checkout_path, self.subdir)
+                if not os.path.isdir(checkout_path):
+                    self.log.error('Subdirectory %s does not exist',
+                                   self.subdir, extra=dict(phase='failure'))
                     sys.exit(1)
 
             os.chdir(checkout_path)

tests/test_subdir.py

@@ -2,28 +2,31 @@
 Test if the subdirectory is correctly navigated to
 """
 import logging
-from os.path import abspath, dirname
 
 import pytest
 from repo2docker.app import Repo2Docker
 
-# This is the path to the repo2docker git repository that this file exists in.
-repo_path = dirname(dirname(abspath(__file__)))
+TEST_REPO = "https://github.com/binderhub-ci-repos/repo2docker-subdir-support"
 
 
 def test_subdir(run_repo2docker):
-    argv = ['--subdir', 'tests/conda/simple', repo_path]
+    # Build from a subdirectory
+    # if subdir support is broken this will fail as the instructions in the
+    # root of the test repo are invalid
+    argv = ['--subdir', 'a directory', TEST_REPO]
     run_repo2docker(argv)
 
 
 def test_subdir_invalid(caplog):
-    caplog.set_level(logging.INFO, logger='Repo2Docker')
+    # test an error is raised when requesting a non existent subdir
+    caplog.set_level(logging.INFO)
 
     app = Repo2Docker()
-    argv = ['--subdir', 'tests/conda/invalid', repo_path]
+    argv = ['--subdir', 'invalid-sub-dir', TEST_REPO]
     app.initialize(argv)
     app.debug = True
-    app.run = False
+    # no build implies no run
+    app.build = False
     with pytest.raises(SystemExit) as excinfo:
         app.start()  # Just build the image and do not run it.
 
@@ -31,4 +34,4 @@ def test_subdir_invalid(caplog):
     assert excinfo.value.code == 1
 
     # Can't get this to record the logs?
-    # assert caplog.text == "Subdirectory tests/conda/invalid does not exist"
+    assert caplog.text == "Subdirectory tests/conda/invalid does not exist"