*
   *   private static class FooFactoryForTest {
   *     public static Foo create(String a, String b, int c, boolean d) {
   *       return Foo.builder()
   *           .setA(a)
   *           .setB(b)
   *           .setC(c)
   *           .setD(d)
   *           .build();
   *     }
   *   }
   *
   *   public void testEquals() {
   *     new ClassSanityTester()

====

NOTE: Only Gradle versions 7 or higher can be explicitly targeted by a variant, as support for this was only added in Gradle 7.

First, we declare a separate _source set_ and a _feature variant_ for our Gradle 7 plugin variant.
Then, we do some specific wiring to turn the feature into a proper Gradle plugin variant: