Add tests for formatting "?..". (#848)

No code changes are needed because analyzer parses it as the same
expression, just with a different token lexeme.
diff --git a/test/whitespace/cascades.stmt b/test/whitespace/cascades.stmt
index 4fc7329..03377d2 100644
--- a/test/whitespace/cascades.stmt
+++ b/test/whitespace/cascades.stmt
@@ -142,4 +142,29 @@
   1,
 ]..cascade(() {
     ;
-  });
\ No newline at end of file
+  });
+>>> allow same-line cascades to mix null-aware
+list
+  ?..add("baz")
+  ..add("bar");
+<<<
+list?..add("baz")..add("bar");
+>>> mixed
+foo?..a()..b()..c();
+<<<
+foo
+  ?..a()
+  ..b()
+  ..c();
+>>> null-aware getter
+foo?..baz..baz;
+<<<
+foo
+  ?..baz
+  ..baz;
+>>> null-aware setter
+foo?..baz = 3..baz=5;
+<<<
+foo
+  ?..baz = 3
+  ..baz = 5;
\ No newline at end of file