TST: Move merge/join tests into sub-dir (pandas-dev#18643)

Author: reidy-p

pandas/tests/reshape/merge/__init__.py

@@ -13,7 +13,7 @@
 
 from pandas._libs import join as libjoin
 import pandas.util.testing as tm
-from pandas.tests.reshape.test_merge import get_test_data, N, NGROUPS
+from pandas.tests.reshape.merge.test_merge import get_test_data, N, NGROUPS
 
 
 a_ = np.array

pandas/tests/reshape/data/allow_exact_matches.csv renamed to pandas/tests/reshape/merge/data/allow_exact_matches.csv

@@ -761,6 +761,7 @@ def pxd(name):
                 'pandas.tests.io.formats',
                 'pandas.tests.groupby',
                 'pandas.tests.reshape',
+                'pandas.tests.reshape.merge',
                 'pandas.tests.series',
                 'pandas.tests.scalar',
                 'pandas.tests.tseries',
@@ -800,6 +801,7 @@ def pxd(name):
                     'pandas.tests.io.formats': ['data/*.csv'],
                     'pandas.tests.io.msgpack': ['data/*.mp'],
                     'pandas.tests.reshape': ['data/*.csv'],
+                    'pandas.tests.reshape.merge': ['data/*.csv'],
                     'pandas.tests.tseries.offsets': ['data/*.pickle'],
                     'pandas.io.formats': ['templates/*.tpl']
                     },