feat(build runner): added in context, dockerfile_location

this is a new feature meant to allow people to use any file as
  a dockerfile and any folder as a context directory

buildtrigger/test/test_basehandler.py

@@ -13,3 +13,43 @@ from buildtrigger.basehandler import BuildTriggerHandler
 ])
 def test_path_is_dockerfile(input, output):
   assert BuildTriggerHandler.filename_is_dockerfile(input) == output
+
+
+@pytest.mark.parametrize('input,output', [
+  ("", {}),
+  ("/a", {"/a": ["/"]}),
+  ("a", {"/a": ["/"]}),
+  ("/b/a", {"/b/a": ["/b", "/"]}),
+  ("b/a", {"/b/a": ["/b", "/"]}),
+  ("/c/b/a", {"/c/b/a": ["/c/b", "/c", "/"]}),
+  ("/a//b//c", {"/a/b/c": ["/", "/a", "/a/b"]}),
+  ("/a", {"/a": ["/"]}),
+])
+def test_subdir_path_map_no_previous(input, output):
+  actual_mapping = BuildTriggerHandler.get_parent_directory_mappings(input)
+  for key in actual_mapping:
+    value = actual_mapping[key]
+    actual_mapping[key] = value.sort()
+  for key in output:
+    value = output[key]
+    output[key] = value.sort()
+
+  assert actual_mapping == output
+
+
+@pytest.mark.parametrize('new_path,original_dictionary,output', [
+  ("/a", {}, {"/a": ["/"]}),
+  ("b", {"/a": ["some_path", "another_path"]}, {"/a": ["some_path", "another_path"], "/b": ["/"]}),
+  ("/a/b/c/d", {"/e": ["some_path", "another_path"]},
+   {"/e": ["some_path", "another_path"], "/a/b/c/d": ["/", "/a", "/a/b", "/a/b/c"]}),
+])
+def test_subdir_path_map(new_path, original_dictionary, output):
+  actual_mapping = BuildTriggerHandler.get_parent_directory_mappings(new_path, original_dictionary)
+  for key in actual_mapping:
+    value = actual_mapping[key]
+    actual_mapping[key] = value.sort()
+  for key in output:
+    value = output[key]
+    output[key] = value.sort()
+
+  assert actual_mapping == output