FIX .format arguments were in the wrong order

Add check_no_fit_attributes_set_in_init test and use name in the error
message rather than estimator since the former is more readable.

sklearn/utils/estimator_checks.py

@@ -1416,8 +1416,8 @@ def check_no_fit_attributes_set_in_init(name, Estimator):
                 "By convention, attributes ending with '_' are "
                 'estimated from data in scikit-learn. Consequently they '
                 'should not be initialized in the constructor of an '
-                'estimator but in the fit method. Attribute {0!r} '
-                'was found in estimator {1}'.format(estimator, attr))
+                'estimator but in the fit method. Attribute {!r} '
+                'was found in estimator {}'.format(attr, name))
 
 
 def check_sparsify_coefficients(name, Estimator):

sklearn/utils/tests/test_estimator_checks.py

@@ -7,6 +7,7 @@
 from sklearn.utils.testing import assert_raises_regex, assert_true
 from sklearn.utils.estimator_checks import check_estimator
 from sklearn.utils.estimator_checks import check_estimators_unfitted
+from sklearn.utils.estimator_checks import check_no_fit_attributes_set_in_init
 from sklearn.ensemble import AdaBoostClassifier
 from sklearn.linear_model import MultiTaskElasticNet
 from sklearn.utils.validation import check_X_y, check_array
@@ -154,3 +155,19 @@ def test_check_estimators_unfitted():
     # check that CorrectNotFittedError inherit from either ValueError
     # or AttributeError
     check_estimators_unfitted("estimator", CorrectNotFittedErrorClassifier)
+
+
+def test_check_no_fit_attributes_set_in_init():
+    class NonConformantEstimator(object):
+        def __init__(self):
+            self.you_should_not_set_this_ = None
+
+    msg = ("By convention, attributes ending with '_'.+"
+           'should not be initialized in the constructor.+'
+           "Attribute 'you_should_not_set_this_' was found.+"
+           'in estimator estimator_name')
+
+    assert_raises_regex(AssertionError, msg,
+                        check_no_fit_attributes_set_in_init,
+                        'estimator_name',
+                        NonConformantEstimator)