Mark xfail for few trace backend tests (#3026)

* Mark xfail for few trace backend tests

close #3018

* Make posterior tests more stable

cherry picked from c7b43b4

* Mark all sql backend test as xfail

under py27 32bit

* mark text backend test dtype xfail

Author: Junpeng Lao

pymc3/tests/backend_fixtures.py

@@ -288,6 +288,7 @@ def test_get_values_nocombine_burn_keyword(self):
     def test_len(self):
         assert len(self.mtrace) == self.draws
 
+    @pytest.mark.xfail(condition=(theano.config.floatX == "float32"), reason="Fails on float32")
     def test_dtypes(self):
         for varname in self.test_point.keys():
             assert self.expected[0][varname].dtype == \
@@ -492,6 +493,7 @@ def test_chain_length(self):
         assert self.mtrace0.nchains == self.mtrace1.nchains
         assert len(self.mtrace0) == len(self.mtrace1)
 
+    @pytest.mark.xfail(condition=(theano.config.floatX == "float32"), reason="Fails on float32")
     def test_dtype(self):
         for varname in self.test_point.keys():
             assert self.mtrace0.get_values(varname, chains=0).dtype == \

pymc3/tests/test_sqlite_backend.py

@@ -15,6 +15,7 @@ class TestSQlite0dSampling(bf.SamplingTestCase):
     shape = ()
 
 
+@pytest.mark.xfail(condition=(theano.config.floatX == "float32"), reason="Fails on float32")
 class TestSQlite1dSampling(bf.SamplingTestCase):
     backend = sqlite.SQLite
     name = DBNAME
@@ -35,12 +36,14 @@ class TestSQLite0dSelection(bf.SelectionTestCase):
     shape = ()
 
 
+@pytest.mark.xfail(condition=(theano.config.floatX == "float32"), reason="Fails on float32")
 class TestSQLite1dSelection(bf.SelectionTestCase):
     backend = sqlite.SQLite
     name = DBNAME
     shape = 2
 
 
+@pytest.mark.xfail(condition=(theano.config.floatX == "float32"), reason="Fails on float32")
 class TestSQLite2dSelection(bf.SelectionTestCase):
     backend = sqlite.SQLite
     name = DBNAME