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


I assume that I am missing something. But what?