Add error handling tests

tests/minimal_config.yaml

@@ -0,0 +1,15 @@
+---
+remote: '/var/empty'
+key: 0x00000000
+
+images:
+  rootfs-minimal:
+    target: ve/docker
+    kinds:
+    - tar.xz
+
+branches:
+  Sisyphus:
+    arches:
+      x86_64:
+...

tests/test_errors.py

@@ -0,0 +1,59 @@
+from unittest import TestCase
+
+import shutil
+import tempfile
+
+import yaml
+
+from cloud_build import CB
+from cloud_build import Error
+
+
+def update(old_dict, kwargs):
+    new_dict = old_dict.copy()
+    for key, value in kwargs.items():
+        if value is None:
+            del new_dict[key]
+        else:
+            new_dict[key] = value
+    return new_dict
+
+
+class TestErrors(TestCase):
+    def setUp(self):
+        kwargs = {}
+        kwargs['data_dir'] = tempfile.mkdtemp(prefix='cloud_build')
+        self.kwargs = kwargs
+
+    def tearDown(self):
+        shutil.rmtree(self.kwargs['data_dir'])
+
+    def test_read_config_not_found(self):
+        regex = 'config file.*No such file or directory'
+        self.kwargs.update(config='/var/empty/cb_conf.yaml')
+        self.assertRaisesRegex(Error, regex, CB, **self.kwargs)
+
+    def test_read_config_permission_denied(self):
+        regex = 'config file.*Permission denied'
+        self.kwargs.update(config='/root/cb_conf.yaml')
+        self.assertRaisesRegex(Error, regex, CB, **self.kwargs)
+
+    def test_required_parameters_in_config(self):
+        config = tempfile.mktemp(prefix='cb_conf')
+        with open('tests/minimal_config.yaml') as f:
+            cfg = yaml.safe_load(f)
+
+        parameter = 'key'
+        for parameter in ['remote', 'key', 'images', 'branches']:
+            with open(config, 'w') as f:
+                yaml.safe_dump(update(cfg, {parameter: None}), f)
+
+            regex = f'parameter.*{parameter}'
+            self.kwargs.update(config=config)
+            self.assertRaisesRegex(Error, regex, CB, **self.kwargs)
+
+    def test_run_already_running(self):
+        self.kwargs.update(config='tests/minimal_config.yaml')
+        cb = CB(**self.kwargs)  # noqa F841
+        regex = 'already running'
+        self.assertRaisesRegex(Error, regex, CB, **self.kwargs)