#3057. Add instance check tests

TypeSystem/flow-analysis/reachability_A12_t01.dart

@@ -14,13 +14,13 @@
 /// the case `T` is `R?` and `Null <: S`.
 /// @author [email protected]
 
+import '../../Utils/static_type_helper.dart';
+
 main() {
   int? i = 2 > 1 ? null : 42;
   if (i is Null) {
-    Null n = i; // Ok
-    int j = i;
-//          ^
-// [analyzer] unspecified
-// [cfe] unspecified
+    Null n = i;
+  } else {
+    i.expectStaticType<Exactly<int>>();
   }
 }

TypeSystem/flow-analysis/reachability_A12_t02.dart

@@ -11,16 +11,16 @@
 /// @description Checks that for expression of the form `E1 is S`
 /// `true(N) = promote(E1, S, after(E1))` and
 /// `false(N) = promote(E1, factor(T, S), after(E1))`. Test `factor(T, S)` for
-/// the case `T` is `R?` and `Null <: S`.
+/// the case `T` is `R?` and `S` is not subtype of `Null`.
 /// @author [email protected]
 
+import '../../Utils/static_type_helper.dart';
+
 main() {
   int? i = 2 > 1 ? null : 42;
   if (i is int) {
     int j = i;
-    Null n = i;
-//           ^
-// [analyzer] unspecified
-// [cfe] unspecified
+  } else {
+    i.expectStaticType<Exactly<Null>>();
   }
 }

TypeSystem/flow-analysis/reachability_A12_t03.dart

@@ -22,13 +22,12 @@ class C {
 
 test(FutureOr<C> foc) async {
   if (foc is Future<C>) {
+  } else {
     foc.foo();
-//      ^^^
-// [analyzer] unspecified
-// [cfe] unspecified
   }
 }
 
 main() {
-  print(test);
+  test(C());
+  test(Future<C>.value(C()));
 }

TypeSystem/flow-analysis/reachability_A12_t04.dart

@@ -15,14 +15,16 @@
 /// @author [email protected]
 
 import 'dart:async';
+import '../../Utils/static_type_helper.dart';
 
 class C {
   void foo() {}
 }
 
 test(FutureOr<C> foc) async {
   if (foc is C) {
-    foc.foo(); // Ok
+  } else {
+    foc.expectStaticType<Exactly<Future<C>>>();
   }
 }