Add tests and fix empty config handling

dbms/tests/integration/test_relative_filepath/configs/config.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0"?>
+<yandex>
+    <user_files_path>user_files</user_files_path>
+</yandex>

dbms/tests/integration/test_relative_filepath/test.py

@@ -0,0 +1,33 @@
+import pytest
+
+from helpers.cluster import ClickHouseCluster
+
+cluster = ClickHouseCluster(__file__)
+node = cluster.add_instance('node')
+path_to_userfiles_from_defaut_config = "user_files"
+
+@pytest.fixture(scope="module")
+def start_cluster():
+    try:
+        cluster.start()
+        yield cluster
+    finally:
+        cluster.shutdown()
+
+def test_filepath(start_cluster):
+    # 2 rows data
+    some_data = "\t111.222\nData\t333.444"
+
+    node.exec_in_container(['bash', '-c', 'echo "{}{}" > {}'.format(
+        filename,
+        some_data,
+        path_to_userfiles_from_defaut_config + "/relative_user_file_test"
+    )], privileged=True, user='root')
+
+    test_requests = [("relative_user_file_test", "2"),
+                     ("../" + path_to_userfiles_from_defaut_config + "relative_user_file_test", "2")]
+
+    for pattern, value in test_requests:
+        assert node.query('''
+            select count(*) from file('strange_names/{}', 'TSV', 'text String, number Float64')
+        '''.format(pattern)) == '{}\n'.format(value)