Add test case handling NoReturn stub and top-level methods (exit)

Fixes https://github.com/icy-arctic-fox/spectator/issues/29

spec/issues/github_issue_29_spec.cr

@@ -0,0 +1,20 @@
+require "../spec_helper"
+
+Spectator.describe "GitHub Issue #29" do
+  class SomeClass
+    def goodbye
+      exit 0
+    end
+  end
+
+  mock SomeClass do
+    stub exit(code)
+  end
+
+  describe SomeClass do
+    it "captures exit" do
+      expect(subject).to receive(:exit).with(0)
+      subject.goodbye
+    end
+  end
+end