1 files changed, 16 insertions, 0 deletions
diff --git a/tests/regressiontests/forms/formsets.py b/tests/regressiontests/forms/formsets.py
index 700ab7c358..d9d4082f71 100644
--- a/tests/regressiontests/forms/formsets.py
+++ b/tests/regressiontests/forms/formsets.py
@@ -621,4 +621,20 @@ Make sure the management form has the correct prefix.
 >>> formset.management_form.prefix
 'form'
 
+# Regression test for #12878 #################################################
+
+>>> data = {
+...     'drinks-TOTAL_FORMS': '2', # the number of forms rendered
+...     'drinks-INITIAL_FORMS': '0', # the number of forms with initial data
+...     'drinks-MAX_NUM_FORMS': '0', # max number of forms
+...     'drinks-0-name': 'Gin and Tonic',
+...     'drinks-1-name': 'Gin and Tonic',
+... }
+
+>>> formset = FavoriteDrinksFormSet(data, prefix='drinks')
+>>> formset.is_valid()
+False
+>>> print formset.non_form_errors()
+<ul class="errorlist"><li>You may only specify a drink once.</li></ul>
+
 """