1 files changed, 26 insertions, 0 deletions
diff --git a/spec/mspec/lib/mspec/matchers/be_an_instance_of.rb b/spec/mspec/lib/mspec/matchers/be_an_instance_of.rb
new file mode 100644
index 0000000000..6e31afcddd
--- /dev/null
+++ b/spec/mspec/lib/mspec/matchers/be_an_instance_of.rb
@@ -0,0 +1,26 @@
+class BeAnInstanceOfMatcher
+  def initialize(expected)
+    @expected = expected
+  end
+
+  def matches?(actual)
+    @actual = actual
+    @actual.instance_of?(@expected)
+  end
+
+  def failure_message
+    ["Expected #{@actual.inspect} (#{@actual.class})",
+     "to be an instance of #{@expected}"]
+  end
+
+  def negative_failure_message
+    ["Expected #{@actual.inspect} (#{@actual.class})",
+     "not to be an instance of #{@expected}"]
+  end
+end
+
+class Object
+  def be_an_instance_of(expected)
+    BeAnInstanceOfMatcher.new(expected)
+  end
+end