Output deprecation warning when at_least(0) is sent

See rspec#133

lib/rspec/mocks/message_expectation.rb

@@ -302,6 +302,12 @@ def exactly(n, &block)
       #
       #   dealer.should_receive(:deal_card).at_least(9).times
       def at_least(n, &block)
+        if n == 0
+          RSpec::Mocks.warn_deprecation <<-MSG
+DEPRECATION: at_least(0) is deprecated. Use #stub instead of #should_receive. Called from #{caller(0)[1]}
+MSG
+        end
+
         @implementation = block if block
         set_expected_received_count :at_least, n
         self

spec/rspec/mocks/at_least_spec.rb

@@ -97,31 +97,35 @@ module Mocks
         @double.rspec_verify
       end
 
-      it "passes with at_least(0) with no return if called once" do
-        @double.should_receive(:do_something).at_least(0).times
-        @double.do_something
-      end
-
-      it "passes with at_least(0) with return block if called once" do
-        @double.should_receive(:do_something).at_least(0).times { true }
-        @double.do_something
-      end
-
-      it "passes with at_least(0) with and_return if called once" do
-        @double.should_receive(:do_something).at_least(0).times.and_return true
-        @double.do_something
-      end
-
-      it "passes with at_least(0) with no return if never called" do
-        @double.should_receive(:do_something).at_least(0).times
-      end
-
-      it "passes with at_least(0) with return block if never called" do
-        @double.should_receive(:do_something).at_least(0).times { true }
-      end
-
-      it "passes with at_least(0) with and_return if never called" do
-        @double.should_receive(:do_something).at_least(0).times.and_return true
+      context "when sent with 0" do
+        before { RSpec::Mocks.should_receive(:warn_deprecation) }
+
+        it "passes with at_least(0) with no return if called once" do
+          @double.should_receive(:do_something).at_least(0).times
+          @double.do_something
+        end
+
+        it "passes with at_least(0) with return block if called once" do
+          @double.should_receive(:do_something).at_least(0).times { true }
+          @double.do_something
+        end
+
+        it "passes with at_least(0) with and_return if called once" do
+          @double.should_receive(:do_something).at_least(0).times.and_return true
+          @double.do_something
+        end
+
+        it "passes with at_least(0) with no return if never called" do
+          @double.should_receive(:do_something).at_least(0).times
+        end
+
+        it "passes with at_least(0) with return block if never called" do
+          @double.should_receive(:do_something).at_least(0).times { true }
+        end
+
+        it "passes with at_least(0) with and_return if never called" do
+          @double.should_receive(:do_something).at_least(0).times.and_return true
+        end
       end
 
       it "uses a stub value if no value set" do