opus: add test

Formula/opus.rb

@@ -29,4 +29,35 @@ class Opus < Formula
     system "./configure", *args
     system "make", "install"
   end
+
+  test do
+    (testpath/"test.cpp").write <<-EOS.undent
+      #include <opus.h>
+
+      int main(int argc, char **argv)
+      {
+        int err = 0;
+        opus_int32 rate = 48000;
+        int channels = 2;
+        int app = OPUS_APPLICATION_AUDIO;
+        OpusEncoder *enc;
+        int ret;
+
+        enc = opus_encoder_create(rate, channels, app, &err);
+        if (!(err < 0))
+        {
+          err = opus_encoder_ctl(enc, OPUS_SET_BITRATE(OPUS_AUTO));
+          if (!(err < 0))
+          {
+             opus_encoder_destroy(enc);
+             return 0;
+          }
+        }
+        return err;
+      }
+    EOS
+    system ENV.cxx, "-I#{include}/opus", "-L#{lib}", "-lopus",
+           testpath/"test.cpp", "-o", "test"
+    system "./test"
+  end
 end