added specific test

Author: Tom Augspurger

pandas/tests/extension/test_format.py

@@ -0,0 +1,44 @@
+import pandas as pd
+
+
+class MyDtype(pd.api.extensions.ExtensionDtype):
+    name = "mydtype"
+    type = list
+
+
+class MyEA(pd.api.extensions.ExtensionArray):
+    def __init__(self, data):
+        self.data = data
+        self._dtype = MyDtype()
+
+    @property
+    def dtype(self):
+        return self._dtype
+
+    def __len__(self):
+        return 1
+
+    def __array__(self, dtype=None):
+        raise ValueError("Cannot be converted to an array!")
+
+    def _format_array(
+        self,
+        formatter: None,
+        float_format: None,
+        na_rep="NaN",
+        digits=None,
+        space=None,
+        justify="right",
+        decimal=".",
+        leading_space=True,
+        quoting=None,
+    ):
+        return ["<MyEA>([1])"]
+
+
+def test_no_conversion():
+    s = pd.Series(MyEA([1]))
+    repr(s)  # OK!
+
+    df = pd.DataFrame({"A": MyEA([1])}, copy=False)
+    repr(df)  # OK!