Document validate-borgmatic-config and add a few tests.

tests/end-to-end/test_validate_config.py

@@ -0,0 +1,36 @@
+import os
+import subprocess
+import tempfile
+
+
+def test_validate_config_command_with_valid_configuration_succeeds():
+    with tempfile.TemporaryDirectory() as temporary_directory:
+        config_path = os.path.join(temporary_directory, 'test.yaml')
+
+        subprocess.check_call(
+            'generate-borgmatic-config --destination {}'.format(config_path).split(' ')
+        )
+        exit_code = subprocess.call(
+            'validate-borgmatic-config --config {}'.format(config_path).split(' ')
+        )
+
+        assert exit_code == 0
+
+
+def test_validate_config_command_with_invalid_configuration_fails():
+    with tempfile.TemporaryDirectory() as temporary_directory:
+        config_path = os.path.join(temporary_directory, 'test.yaml')
+
+        subprocess.check_call(
+            'generate-borgmatic-config --destination {}'.format(config_path).split(' ')
+        )
+        config = open(config_path).read().replace('keep_daily: 7', 'keep_daily: "7"')
+        config_file = open(config_path, 'w')
+        config_file.write(config)
+        config_file.close()
+
+        exit_code = subprocess.call(
+            'validate-borgmatic-config --config {}'.format(config_path).split(' ')
+        )
+
+        assert exit_code == 1