Adds test to catch optional config being required

Closes jupyterhub#80

tests/conftest.py

@@ -1,4 +1,5 @@
 import os
+import shutil
 import tempfile
 from distutils.dir_util import copy_tree
 
@@ -38,3 +39,18 @@ def git_repo(monkeypatch):
         r.index.commit("initial commit")
 
         yield r
+
+@pytest.fixture(scope="function")
+def git_repo_bare_minimum(monkeypatch, git_repo):
+    """
+    This fixture modifies the default git_repo fixture to use another the
+    chartpress_bare_minimum.yaml as chartpress.yaml and removes the image
+    directory.
+    """
+    r = git_repo
+    shutil.move("chartpress_bare_minimum.yaml", "chartpress.yaml")
+    shutil.rmtree("image")
+    r.git.add(all=True)
+    r.index.commit("bare minimum commit")
+
+    yield r

tests/test_helm_chart/chartpress_bare_minimum.yaml

@@ -0,0 +1,2 @@
+charts:
+  - name: testchart

tests/test_repo_interactions.py

@@ -216,6 +216,20 @@ def test_chartpress_paths_configuration(git_repo, capfd):
     assert f"Updating testchart/values.yaml: image: testchart/testimage:{tag}" in out
 
 
+def test_chartpress_run_bare_minimum(git_repo_bare_minimum, capfd):
+    """
+    Ensures that chartpress will run with a minimal configuration of only
+    providing a single chart name. This can catch errors that assumes we need to
+    have a images key in the chartpress.yaml configuration for example.
+    """
+    r = git_repo_bare_minimum
+    sha = r.heads.master.commit.hexsha[:7]
+    tag = f"0.0.1-002.{sha}"
+
+    out = _capture_output([], capfd)
+    assert f"Updating testchart/Chart.yaml: version: {tag}" in out
+
+
 def _capture_output(args, capfd):
     """
     Calls chartpress given provided arguments and captures the output during the