error when attempting unittest

[Patrick Tinkham]

When I try to compile a unittest on the following:

import std.stdio;
class A {
   int x = 42;
}

unittest {
   auto a1 = new A;
   assert (a1.x == 42);
   auto a2 = a1;
   a2.x = 100;
   assert (a1.x == 100);
}

I get the following:

patrick at patrick-desktop:~/d$ rdmd --main -unittest c.d
/usr/bin/ld: cannot find -lcurl
collect2: ld returned 1 exit status
--- errorlevel 1
patrick at patrick-desktop:~/d$


I assume that I am missing something. But what?