From 687906efdaa29ecf4a296f331855819dae31447a Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Sat, 12 Sep 2020 04:13:11 -0400
Subject: [PATCH 1/2] Add some tests for cbook._define_aliases.

---
 lib/matplotlib/tests/test_cbook.py | 33 ++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/lib/matplotlib/tests/test_cbook.py b/lib/matplotlib/tests/test_cbook.py
index de99701d7757..f06b8965f91f 100644
--- a/lib/matplotlib/tests/test_cbook.py
+++ b/lib/matplotlib/tests/test_cbook.py
@@ -298,6 +298,39 @@ def test_sanitize_sequence():
     assert k == cbook.sanitize_sequence(k)
 
 
+def test_define_aliases():
+    @cbook._define_aliases({'prop': ['alias1', 'alias2']})
+    class NoGetter:
+        def set_prop(self):
+            pass
+
+    @cbook._define_aliases({'prop': ['alias1', 'alias2']})
+    class NoSetter:
+        def get_prop(self):
+            pass
+
+    assert getattr(NoGetter, 'get_alias1', None) is None
+    assert getattr(NoGetter, 'set_alias1', None) is not None
+    assert getattr(NoGetter, 'get_alias2', None) is None
+    assert getattr(NoGetter, 'set_alias2', None) is not None
+    assert NoGetter._alias_map == {'prop': ['alias1', 'alias2']}
+
+    assert getattr(NoSetter, 'get_alias1', None) is not None
+    assert getattr(NoSetter, 'set_alias1', None) is None
+    assert getattr(NoSetter, 'get_alias2', None) is not None
+    assert getattr(NoSetter, 'set_alias2', None) is None
+    assert NoSetter._alias_map == {'prop': ['alias1', 'alias2']}
+
+
+def test_define_aliases_invalid():
+    class Invalid:
+        pass
+
+    with pytest.raises(ValueError,
+                       match="Neither getter nor setter exists for 'prop'"):
+        cbook._define_aliases({'prop': ['alias1', 'alias2']})(Invalid)
+
+
 fail_mapping = (
     ({'a': 1}, {'forbidden': ('a')}),
     ({'a': 1}, {'required': ('b')}),

From 43a4cf11dc1e40ba0a1f22a1a682d89d74b8fabe Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Sat, 12 Sep 2020 04:26:33 -0400
Subject: [PATCH 2/2] Add test of subclassing with cbook._define_aliases.

---
 lib/matplotlib/tests/test_cbook.py | 42 ++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/lib/matplotlib/tests/test_cbook.py b/lib/matplotlib/tests/test_cbook.py
index f06b8965f91f..0ecc3f25ef28 100644
--- a/lib/matplotlib/tests/test_cbook.py
+++ b/lib/matplotlib/tests/test_cbook.py
@@ -331,6 +331,48 @@ class Invalid:
         cbook._define_aliases({'prop': ['alias1', 'alias2']})(Invalid)
 
 
+def test_define_aliases_subclass():
+    @cbook._define_aliases({'prop': ['alias']})
+    class Base:
+        def __init__(self):
+            self.call_count = {'Base:set_prop': 0}
+
+        def set_prop(self):
+            self.call_count['Base:set_prop'] += 1
+
+    class Derived(Base):
+        def __init__(self):
+            super().__init__()
+            self.call_count['Derived:set_prop'] = 0
+
+        def set_prop(self):
+            self.call_count['Derived:set_prop'] += 1
+
+    # Calling original or alias should run the same method.
+    b = Base()
+    b.set_prop()
+    assert b.call_count['Base:set_prop'] == 1
+    b.set_alias()
+    assert b.call_count['Base:set_prop'] == 2
+
+    d = Derived()
+    # Calling original or alias should run the same derived method.
+    d.set_prop()
+    assert d.call_count['Base:set_prop'] == 0
+    assert d.call_count['Derived:set_prop'] == 1
+    d.set_alias()
+    assert d.call_count['Base:set_prop'] == 0
+    assert d.call_count['Derived:set_prop'] == 2
+
+    # Calling original or alias should run the same base method.
+    Base.set_prop(d)
+    assert d.call_count['Base:set_prop'] == 1
+    assert d.call_count['Derived:set_prop'] == 2
+    Base.set_alias(d)
+    assert d.call_count['Base:set_prop'] == 2
+    assert d.call_count['Derived:set_prop'] == 2
+
+
 fail_mapping = (
     ({'a': 1}, {'forbidden': ('a')}),
     ({'a': 1}, {'required': ('b')}),