Move PytestExerimentalApiWarning to warning_types

src/_pytest/experiments.py

@@ -1,13 +0,0 @@
-class PytestExerimentalApiWarning(FutureWarning):
-    "warning category used to denote experiments in pytest"
-
-    @classmethod
-    def simple(cls, apiname):
-        return cls(
-            "{apiname} is an experimental api that may change over time".format(
-                apiname=apiname
-            )
-        )
-
-
-PYTESTER_COPY_EXAMPLE = PytestExerimentalApiWarning.simple("testdir.copy_example")

src/_pytest/pytester.py

@@ -642,10 +642,12 @@ class Testdir(object):
         return p
 
     def copy_example(self, name=None):
-        from . import experiments
         import warnings
 
-        warnings.warn(experiments.PYTESTER_COPY_EXAMPLE, stacklevel=2)
+        warnings.warn(
+            pytest.PytestExerimentalApiWarning.simple("testdir.copy_example"),
+            stacklevel=2,
+        )
         example_dir = self.request.config.getini("pytester_example_dir")
         if example_dir is None:
             raise ValueError("pytester_example_dir is unset, can't copy examples")

src/_pytest/warning_types.py

@@ -20,3 +20,20 @@ class RemovedInPytest4Warning(PytestDeprecationWarning):
 
     Warning class for features scheduled to be removed in pytest 4.0.
     """
+
+
+class PytestExerimentalApiWarning(PytestWarning, FutureWarning):
+    """
+    Bases: :class:`pytest.PytestWarning`, :class:`FutureWarning`.
+
+    Warning category used to denote experiments in pytest. Use sparingly as the API might change or even be
+    removed completely in future version
+    """
+
+    @classmethod
+    def simple(cls, apiname):
+        return cls(
+            "{apiname} is an experimental api that may change over time".format(
+                apiname=apiname
+            )
+        )