Fix comma separated string in "Bindings" (#797)

tests/test_binding.py

@@ -0,0 +1,31 @@
+import pytest
+
+from textual.binding import Bindings, Binding
+
+BINDING1 = Binding("a,b", action="action1", description="description1")
+BINDING2 = Binding("c", action="action2", description="description2")
+
+
+@pytest.fixture
+def bindings():
+    yield Bindings([BINDING1, BINDING2])
+
+
+def test_bindings_get_key(bindings):
+    assert bindings.get_key("b") == Binding("b", action="action1", description="description1")
+    assert bindings.get_key("c") == BINDING2
+
+
+def test_bindings_merge_simple(bindings):
+    left = Bindings([BINDING1])
+    right = Bindings([BINDING2])
+    assert Bindings.merge([left, right]).keys == bindings.keys
+
+
+def test_bindings_merge_overlap():
+    left = Bindings([BINDING1])
+    another_binding = Binding("a", action="another_action", description="another_description")
+    assert Bindings.merge([left, Bindings([another_binding])]).keys == {
+        "a": another_binding,
+        "b": Binding("b", action="action1", description="description1"),
+    }