initial tests for composing roles with stubbed methods

S14-roles/stubs.t

@@ -0,0 +1,22 @@
+use v6;
+use Test;
+
+plan 6;
+
+role WithStub { method a() { ... } };
+role ProvidesStub1 { method a() { 1 } };
+role ProvidesStub2 { method a() { 2 } };
+
+dies_ok  { eval 'class A does WithStub { }' },
+        'need to implement stubbed methods at role-into-class composition time';
+lives_ok { eval 'role B does WithStub { }' },
+        'but roles are fine';
+lives_ok { eval 'class C does WithStub { method a() { 3 } }' },
+        'directly implementing the stubbed method is fine';
+lives_ok { eval 'class D does WithStub does ProvidesStub1 { }' },
+        'composing the stubbed method is fine';
+dies_ok  { eval 'class E does WithStub does ProvidesStub1 does ProvidesStub2 { }' },
+        'composing stub and 2 implementations dies again';
+lives_ok { eval 'class F does WithStub does ProvidesStub1 does ProvidesStub2 {
+    method a() { 4 } }' },
+        'composing stub and 2 implementations allows custom implementation';