Move data_directory fixture to toplevel conftest

This is the default where [datamgr](https://github.com/ibis-
project/ibis/blob/master/ci/datamgr.py#L208) initializes the SQLite
db.

Author: Krisztián Szűcs <szucs.krisztian@gmail.com>

Closes #1581 from kszucs/sqlite_default_path and squashes the following commits:

eeef5ae [Krisztián Szűcs] move data_directory fixture to top level conftest

conftest.py

@@ -1,6 +1,10 @@
 import fnmatch
 import os
 import sys
+import pytest
+
+from ibis.compat import Path
+
 
 collect_ignore = ['setup.py']
 
@@ -11,3 +15,17 @@
         for filename in filenames:
             if fnmatch.fnmatch(filename, '*.py'):
                 collect_ignore.append(os.path.join(root, filename))
+
+
+@pytest.fixture(scope='session')
+def data_directory():
+    root = Path(__file__).absolute().parent
+
+    default = root / 'ci' / 'ibis-testing-data'
+    datadir = os.environ.get('IBIS_TEST_DATA_DIRECTORY', default)
+    datadir = Path(datadir)
+
+    if not datadir.exists():
+        pytest.skip('test data directory not found')
+
+    return datadir

ibis/sql/sqlite/tests/conftest.py

@@ -6,10 +6,9 @@
 
 
 @pytest.fixture(scope='module')
-def dbpath():
-    # If we haven't defined an environment variable with the path of the SQLite
-    # database, assume it's in $PWD
-    path = os.environ.get('IBIS_TEST_SQLITE_DATABASE', 'ibis_testing.db')
+def dbpath(data_directory):
+    default = str(data_directory / 'ibis_testing.db')
+    path = os.environ.get('IBIS_TEST_SQLITE_DATABASE', default)
     if not os.path.exists(path):
         pytest.skip('SQLite testing db {} does not exist'.format(path))
     else:

ibis/tests/all/conftest.py

@@ -1,8 +1,6 @@
-import os
 import sys
 import pytest
 
-from ibis.compat import Path
 from ibis.tests.backends import (Csv, Parquet, Pandas,
                                  SQLite, Postgres, MySQL, MapD,
                                  Clickhouse, Impala, BigQuery)
@@ -26,20 +24,6 @@
     params_backend.append(pytest.param(MapD, marks=pytest.mark.mapd))
 
 
-@pytest.fixture(scope='session')
-def data_directory():
-    root = Path(__file__).absolute().parents[3]
-
-    default = root / 'ci' / 'ibis-testing-data'
-    datadir = os.environ.get('IBIS_TEST_DATA_DIRECTORY', default)
-    datadir = Path(datadir)
-
-    if not datadir.exists():
-        pytest.skip('test data directory not found')
-
-    return datadir
-
-
 @pytest.fixture(params=params_backend, scope='session')
 def backend(request, data_directory):
     return request.param(data_directory)