nettle: add test

Closes Homebrew/homebrew#35314.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/nettle.rb

@@ -22,4 +22,32 @@ class Nettle < Formula
     system "make", "install"
     system "make", "check"
   end
+
+  test do
+    (testpath/"test.c").write <<-EOS.undent
+      #include <nettle/sha1.h>
+      #include <stdio.h>
+
+      int main()
+      {
+        struct sha1_ctx ctx;
+        uint8_t digest[SHA1_DIGEST_SIZE];
+        unsigned i;
+
+        sha1_init(&ctx);
+        sha1_update(&ctx, 4, "test");
+        sha1_digest(&ctx, SHA1_DIGEST_SIZE, digest);
+
+        printf("SHA1(test)=");
+
+        for (i = 0; i<SHA1_DIGEST_SIZE; i++)
+          printf("%02x", digest[i]);
+
+        printf("\\n");
+        return 0;
+      }
+    EOS
+    system ENV.cc, "test.c", "-lnettle", "-o", "test"
+    system "./test"
+  end
 end