Code cleanup and tests

testing/resources/docker_hooks_repo/Dockerfile

@@ -0,0 +1,3 @@
+FROM cogniteev/echo
+
+CMD ["echo", "This is overwritten by the hooks.yaml 'entry'"]

testing/resources/docker_hooks_repo/hooks.yaml

@@ -0,0 +1,11 @@
+-   id: docker-hook
+    name: Docker test hook
+    entry: echo
+    language: docker
+    files: \.txt$
+
+-   id: docker-hook-failing
+    name: Docker test hook with nonzero exit code
+    entry: bork
+    language: docker
+    files: \.txt$

testing/util.py

@@ -6,6 +6,7 @@ import shutil
 import jsonschema
 import pytest
 
+from pre_commit.languages.docker import docker_is_running
 from pre_commit.util import cmd_output
 from pre_commit.util import cwd
 
@@ -57,6 +58,11 @@ def cmd_output_mocked_pre_commit_home(*args, **kwargs):
     return cmd_output(*args, env=env, **kwargs)
 
 
+skipif_cant_run_docker = pytest.mark.skipif(
+    docker_is_running() is False,
+    reason='Docker isn\'t running or can\'t  be accessed'
+)
+
 skipif_slowtests_false = pytest.mark.skipif(
     os.environ.get('slowtests') == 'false',
     reason='slowtests=false',