diff --git a/TypeSystem/flow-analysis/type_of_interest_A01_t01.dart b/TypeSystem/flow-analysis/type_of_interest_A01_t01.dart
new file mode 100644
index 0000000000..1831fec3ba
--- /dev/null
+++ b/TypeSystem/flow-analysis/type_of_interest_A01_t01.dart
@@ -0,0 +1,24 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion We say that at type `T` is a type of interest for a variable `x`
+/// in a set of tested types `tested` if `tested` contains a type `S` such that
+/// `T` is `S`, or `T` is `NonNull(S)`.
+///
+/// @description Checks that `x is T` makes `T` a type of interest for `x`.
+/// @author sgrekhov22@gmail.com
+/// @issue 60479
+
+class S {}
+
+class T extends S {
+  int foo() => 42;
+}
+
+main() {
+  S x = S();
+  x is T;  // make `T` a type of interest
+  x = T();
+  x.foo();
+}
diff --git a/TypeSystem/flow-analysis/type_of_interest_A01_t02.dart b/TypeSystem/flow-analysis/type_of_interest_A01_t02.dart
new file mode 100644
index 0000000000..471b58a0c2
--- /dev/null
+++ b/TypeSystem/flow-analysis/type_of_interest_A01_t02.dart
@@ -0,0 +1,33 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion We say that at type `T` is a type of interest for a variable `x`
+/// in a set of tested types `tested` if `tested` contains a type `S` such that
+/// `T` is `S`, or `T` is `NonNull(S)`.
+///
+/// @description Checks that `x is T` makes `T` a type of interest for `x`.
+/// @author sgrekhov22@gmail.com
+
+class S {}
+
+class T extends S {
+  int foo() => 42;
+}
+
+test1(S s) {
+  if (s is T) {}  // make `T` a type of interest
+  s = T();
+  s.foo();
+}
+
+test2(S? s) {
+  if (s is T) {}
+  s = T();
+  s.foo();
+}
+
+main() {
+  test1(S());
+  test2(S());
+}
diff --git a/TypeSystem/flow-analysis/type_of_interest_A01_t03.dart b/TypeSystem/flow-analysis/type_of_interest_A01_t03.dart
new file mode 100644
index 0000000000..b7c2fd20f4
--- /dev/null
+++ b/TypeSystem/flow-analysis/type_of_interest_A01_t03.dart
@@ -0,0 +1,40 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion We say that at type `T` is a type of interest for a variable `x`
+/// in a set of tested types `tested` if `tested` contains a type `S` such that
+/// `T` is `S`, or `T` is `NonNull(S)`.
+///
+/// @description Checks that `x is T?` makes `T` a type of interest for `x`.
+/// @author sgrekhov22@gmail.com
+
+class S {}
+
+class T extends S {
+  int foo() => 42;
+}
+
+test1(S? s) {
+  if (s is T?) {}  // make `T?` and `T` types of interest
+  s = T();
+  s.foo();
+}
+
+test2(S? s) {
+  if (s is T?) {}
+  s = 1 > 2 ? null: T(); // assign `T?` to `s`
+  s?.foo();
+}
+
+test3(S s) {
+  if (s is T?) {}
+  s = T();
+  s.foo();
+}
+
+main() {
+  test1(S());
+  test2(S());
+  test3(S());
+}
diff --git a/TypeSystem/flow-analysis/type_of_interest_A01_t04.dart b/TypeSystem/flow-analysis/type_of_interest_A01_t04.dart
new file mode 100644
index 0000000000..c80bd1d64d
--- /dev/null
+++ b/TypeSystem/flow-analysis/type_of_interest_A01_t04.dart
@@ -0,0 +1,30 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion We say that at type `T` is a type of interest for a variable `x`
+/// in a set of tested types `tested` if `tested` contains a type `S` such that
+/// `T` is `S`, or `T` is `NonNull(S)`.
+///
+/// @description Checks that if `T` is a type of interest for a variable `x`,
+/// then it doesn't make `T?` a type of interest for `x`.
+/// @author sgrekhov22@gmail.com
+
+class S {}
+
+class T extends S {
+  int foo() => 42;
+}
+
+test(S? s) {
+  if (s is T) {}
+  s = 1 > 2 ? null: T(); // assign `T?` to `s`
+  s?.foo();
+//   ^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  print(test);
+}
diff --git a/TypeSystem/flow-analysis/type_of_interest_A02_t01.dart b/TypeSystem/flow-analysis/type_of_interest_A02_t01.dart
new file mode 100644
index 0000000000..94d4c45356
--- /dev/null
+++ b/TypeSystem/flow-analysis/type_of_interest_A02_t01.dart
@@ -0,0 +1,35 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion We say that at type `T` is a type of interest for a variable `x`
+/// in a set of tested types `tested` if `tested` contains a type `S` such that
+/// `T` is `S`, or `T` is `NonNull(S)`.
+///
+/// @description Checks that `x is! T` makes `T` a type of interest for `x`.
+/// @author sgrekhov22@gmail.com
+/// @issue 60479
+
+class S {}
+
+class T extends S {
+  int foo() => 42;
+}
+
+test1() {
+  S s = S();
+  s is! T;  // Make `T` a type of interest
+  s = T();
+  s.foo();
+}
+
+test2(S? s) {
+  if (s is! T?) {}
+  s = T();
+  s.foo();
+}
+
+main() {
+  test1();
+  test2(S());
+}