add explicit log message on failing Docker connection, see #774

repo2docker/app.py

@@ -611,8 +611,11 @@ class Repo2Docker(Application):
             try:
                 docker_client = docker.APIClient(version="auto", **kwargs_from_env())
             except DockerException as e:
-                self.log.exception(e)
+                self.log.error(
+                    "\nDocker client initialization error. Check if docker is running on the host.\n\n"
+                )
                 raise
+
         # If the source to be executed is a directory, continue using the
         # directory. In the case of a local directory, it is used as both the
         # source and target. Reusing a local directory seems better than

tests/unit/test_app.py

@@ -8,6 +8,7 @@ import escapism
 
 from repo2docker.app import Repo2Docker
 from repo2docker.__main__ import make_r2d
+from repo2docker.utils import chdir
 
 
 def test_find_image():
@@ -124,3 +125,24 @@ def test_root_not_allowed():
             builds.return_value = []
             app.build()
         builds.assert_called_once()
+
+
+def test_dryrun_works_without_docker(tmpdir):
+    with chdir(tmpdir):
+        with patch.object(docker, "APIClient") as client:
+            client.side_effect = docker.errors.DockerException("Error: no Docker")
+            app = Repo2Docker(dry_run=True)
+            app.build()
+
+
+def test_error_log_without_docker(tmpdir, caplog):
+    with chdir(tmpdir):
+        with patch.object(docker, "APIClient") as client:
+            client.side_effect = docker.errors.DockerException("Error: no Docker")
+            app = Repo2Docker()
+
+            with pytest.raises(docker.errors.DockerException):
+                app.build()
+
+                captured = capsys.readouterr()
+                assert "Check if docker is running" in captured.err

tests/unit/test_subdir.py

@@ -33,7 +33,7 @@ def test_subdir_in_image_name():
     assert escaped_dirname in app.output_image_spec
 
 
-def test_subdir_invalid(caplog):
+def test_subdir_invalid():
     # test an error is raised when requesting a non existent subdir
     app = Repo2Docker(repo=TEST_REPO, subdir="invalid-sub-dir")
     app.initialize()