fix test and resolve whats new conflit

Author: AntonioAndraues

doc/source/whatsnew/v1.0.0.rst

@@ -371,6 +371,7 @@ Other
 - Bug in :meth:`Series.diff` where a boolean series would incorrectly raise a ``TypeError`` (:issue:`17294`)
 - :meth:`Series.append` will no longer raise a ``TypeError`` when passed a tuple of ``Series`` (:issue:`28410`)
 - Fix corrupted error message when calling ``pandas.libs._json.encode()`` on a 0d array (:issue:`18878`)
+- Bug in :meth:`pandas.io.formats.style.Styler` formatting for floating values not displaying decimals correctly (:issue:`13257`)
 
 .. _whatsnew_1000.contributors:
 

pandas/tests/io/formats/test_style.py

@@ -1189,22 +1189,18 @@ def test_display_subset(self):
             {"a": "{:0.1f}", "b": "{0:.2%}"}, subset=pd.IndexSlice[0, :]
         )._translate()
         expected = "0.1"
-        assert ctx["body"][0][1]["display_value"] == expected
-        assert ctx["body"][1][1]["display_value"] == "1.1234"
-        assert ctx["body"][0][2]["display_value"] == "12.34%"
-
-        raw_11 = "1.1234"
-        ctx = df.style.format("{:0.1f}", subset=pd.IndexSlice[0, :])._translate()
+        raw_11 = "1.123400"
         assert ctx["body"][0][1]["display_value"] == expected
         assert ctx["body"][1][1]["display_value"] == raw_11
-
+        assert ctx["body"][0][2]["display_value"] == "12.34%"
+        
         ctx = df.style.format("{:0.1f}", subset=pd.IndexSlice[0, :])._translate()
         assert ctx["body"][0][1]["display_value"] == expected
         assert ctx["body"][1][1]["display_value"] == raw_11
 
         ctx = df.style.format("{:0.1f}", subset=pd.IndexSlice["a"])._translate()
         assert ctx["body"][0][1]["display_value"] == expected
-        assert ctx["body"][0][2]["display_value"] == "0.1234"
+        assert ctx["body"][0][2]["display_value"] == "0.123400"
 
         ctx = df.style.format("{:0.1f}", subset=pd.IndexSlice[0, "a"])._translate()
         assert ctx["body"][0][1]["display_value"] == expected
@@ -1215,8 +1211,8 @@ def test_display_subset(self):
         )._translate()
         assert ctx["body"][0][1]["display_value"] == expected
         assert ctx["body"][1][1]["display_value"] == "1.1"
-        assert ctx["body"][0][2]["display_value"] == "0.1234"
-        assert ctx["body"][1][2]["display_value"] == "1.1234"
+        assert ctx["body"][0][2]["display_value"] == "0.123400"
+        assert ctx["body"][1][2]["display_value"] == raw_11
 
     def test_display_dict(self):
         df = pd.DataFrame([[0.1234, 0.1234], [1.1234, 1.1234]], columns=["a", "b"])