Keyword argument matcher.

src/matchers/mock.py

@@ -1,13 +1,17 @@
 from itertools import chain
+from numbers import Number
 
 from hamcrest import equal_to
 from hamcrest.core.base_matcher import BaseMatcher
 from hamcrest.core.matcher import Matcher
 from six.moves import zip_longest
 
 
-def call_has_arg(index, expected):
-    return CallHasPositionalArg(index, expected)
+def call_has_arg(arg, expected):
+    if isinstance(arg, Number):
+        return CallHasPositionalArg(arg, expected)
+    else:
+        return CallHasKeywordArg(arg, expected)
 
 
 class CallHasPositionalArg(BaseMatcher):
@@ -38,6 +42,34 @@ def describe_mismatch(self, actual_call, mismatch_description):
             )
 
 
+class CallHasKeywordArg(BaseMatcher):
+    def __init__(self, key, expected):
+        super(CallHasKeywordArg, self).__init__()
+        self.key = key
+        self.expected = expected if isinstance(expected, Matcher) else equal_to(expected)
+
+    def _matches(self, actual_call):
+        args = actual_call[2]
+        return self.key in args and self.expected.matches(args[self.key])
+
+    def describe_to(self, description):
+        description.append_text("mock.call with keyword argument ").append_description_of(self.key).append_text(
+            " matching "
+        )
+        self.expected.describe_to(description)
+
+    def describe_mismatch(self, actual_call, mismatch_description):
+        args = actual_call[2]
+        if self.key in args:
+            mismatch_description.append_text("got mock.call with keyword argument ").append_description_of(
+                self.key
+            ).append_text(" with value ").append_description_of(args[self.key])
+        else:
+            mismatch_description.append_text("got mock.call with without keyword argument ").append_description_of(
+                self.key
+            )
+
+
 def has_call(call_matcher):
     return HasCall(call_matcher)
 

tests/unit/matchers/test_mock.py

@@ -33,8 +33,26 @@ def test_call_has_positional_arg():
 
 
 def test_call_has_keyword_arg():
-    # TODO
-    pass
+    # Given
+    m = MagicMock()
+
+    # When
+    m(f="first", s="second", t="third")
+    call = m.mock_calls[0]
+
+    # Then
+    assert_that(call, call_has_arg("s", "second"))
+    assert_that(call, not_(call_has_arg("s", "nope")))
+    assert_that(call, not_(call_has_arg("w", "nope")))
+    assert_that(call, call_has_arg("s", contains_string("eco")))
+    assert_that(
+        call_has_arg("s", contains_string("eco")),
+        has_string("mock.call with keyword argument 's' matching a string containing 'eco'"),
+    )
+    assert_that(
+        call_has_arg("s", "fifth"), mismatches_with(call, "got mock.call with keyword argument 's' with value 'second'")
+    )
+    assert_that(call_has_arg("n", "nope"), mismatches_with(call, "got mock.call with without keyword argument 'n'"))
 
 
 def test_call_has_args():