Test issues with &await

Closes rakudo/rakudo#1323
Rakudo fix: rakudo/rakudo@c51f1796e6

Include test for both 6.c and 6.d languages, since we use two
separate sets of &awaits for them and each has different failure modes
in the bug.

S17-promise/nonblocking-await.t

@@ -1,7 +1,7 @@
 use v6.d.PREVIEW;
 use Test;
 
-plan 27;
+plan 28;
 
 # Limit scheduler to just 4 real threads, so we'll clearly be needing the
 # non-blocking await support for these to pass.
@@ -271,3 +271,15 @@ PROCESS::<$SCHEDULER> := ThreadPoolScheduler.new(max_threads => 4);
     is @foo.elems, 4, "slips awaited over get flattened out";
   }
 }
+
+{ # https://github.com/rakudo/rakudo/issues/1323
+    # Await must be called in sink context here to trigger the covered bug.
+    # Gymnastics with atomic ints are just to reduce test runtime; the point
+    # of the test is that await awaits in this case for all Promises to
+    # complete instead of just returning immediately.
+    # (same test exists in 6.c tests on purpose; to cover Rakudo impl)
+    my atomicint $x;
+    sub p { start { sleep .3; $x⚛++ } }
+    await [[[p(), [p(), [p(),]]], [p(), p(), p()]], [p(), p(), p()]];
+    is-deeply $x, 9, '&await awaits when given nested containerized iterables';
+}

S17-promise/start.t

@@ -1,7 +1,7 @@
 use v6;
 use Test;
 
-plan 59;
+plan 60;
 
 throws-like { await }, Exception, "a bare await should not work";
 
@@ -248,3 +248,15 @@ lives-ok {
 	});
     nok $wrong, 'No data races on closure interpolation in strings';
 }
+
+{ # https://github.com/rakudo/rakudo/issues/1323
+    # Await must be called in sink context here to trigger the covered bug.
+    # Gymnastics with atomic ints are just to reduce test runtime; the point
+    # of the test is that await awaits in this case for all Promises to
+    # complete instead of just returning immediately.
+    # (same test exists in 6.d tests on purpose; to cover Rakudo impl)
+    my atomicint $x;
+    sub p { start { sleep .3; $x⚛++ } }
+    await [[[p(), [p(), [p(),]]], [p(), p(), p()]], [p(), p(), p()]];
+    is-deeply $x, 9, '&await awaits when given nested containerized iterables';
+}