Add test extra with the same contents as the tests extra.

The `tests` extra will be removed in Plone 7.
`plone.app.testing` was missing because in `tox.ini` we used the not yet existing `test` extra.

news/164.bugfix

@@ -0,0 +1,3 @@
+Add ``test`` extra with the same contents as the ``tests`` extra.
+The ``tests`` extra will be removed in Plone 7.
+[maurits]

setup.py

@@ -20,6 +20,18 @@ def read(*rnames):
     + read("CHANGES.rst")
     + "\n"
 )
+test_requirements = [
+    "plone.app.contenttypes[test]",
+    "plone.app.layout",
+    "plone.app.testing",
+    "plone.autoform",
+    "plone.browserlayer",
+    "plone.supermodel",
+    "plone.testing",
+    "zope.annotation",
+    "zope.intid",
+    "zope.publisher",
+]
 
 setup(
     name="plone.app.z3cform",
@@ -79,17 +91,11 @@ def read(*rnames):
         "Zope",
     ],
     extras_require={
-        "tests": [
-            "plone.app.contenttypes[test]",
-            "plone.app.layout",
-            "plone.app.testing",
-            "plone.autoform",
-            "plone.browserlayer",
-            "plone.supermodel",
-            "plone.testing",
-            "zope.annotation",
-            "zope.intid",
-            "zope.publisher",
-        ]
+        # Until plone.app.z3cform 4.0.2 we only had the 'tests' extra.
+        # In 4.0.3 we introduced the 'test' extra.
+        # Keep 'tests' for backwards compatibility.
+        # Remove it in Plone 7.
+        "test": test_requirements,
+        "tests": test_requirements,
     },
 )