diff --git a/toolchain/check/testdata/class/access/inheritance_friend_access.carbon b/toolchain/check/testdata/class/access/inheritance_friend_access.carbon
new file mode 100644
index 000000000000..a933cc37ac36
--- /dev/null
+++ b/toolchain/check/testdata/class/access/inheritance_friend_access.carbon
@@ -0,0 +1,654 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/none.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/class/access/inheritance_friend_access.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/class/access/inheritance_friend_access.carbon
+
+// --- fail_todo_friend_of_base.carbon
+library "[[@TEST_NAME]]";
+
+class Derived;
+
+base class Base {
+  friend Derived;
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+
+  fn G() {
+    // CHECK:STDERR:        ╭─┤ fail_todo_friend_of_base.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     Self.F();
+    // CHECK:STDERR:        ·     ━━━┳━━
+    // CHECK:STDERR:        ·        ┗━━┫ error: cannot access private member `F` of type `Base`
+    // CHECK:STDERR:        ·           ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    Self.F();
+  }
+}
+
+// --- fail_todo_unqualified_in_friend_of_base.carbon
+library "[[@TEST_NAME]]";
+
+class Derived;
+
+base class Base {
+  friend Derived;
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+
+  fn G() {
+    // CHECK:STDERR:        ╭─┤ fail_todo_unqualified_in_friend_of_base.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     F();
+    // CHECK:STDERR:        ·     ┳
+    // CHECK:STDERR:        ·     ┗━━┫ error: cannot access private member `F` of type `Base`
+    // CHECK:STDERR:        ·        ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    F();
+  }
+}
+
+// --- fail_todo_friend_of_base_via_other_class.carbon
+library "[[@TEST_NAME]]";
+
+class Friend;
+
+base class Base {
+  friend Friend;
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+}
+
+class Friend {
+  fn G(d: Derived) {
+    // CHECK:STDERR:        ╭─┤ fail_todo_friend_of_base_via_other_class.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     d.F();
+    // CHECK:STDERR:        ·     ━┳━
+    // CHECK:STDERR:        ·      ┗━━┫ error: cannot access private member `F` of type `Base`
+    // CHECK:STDERR:        ·         ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    d.F();
+  }
+}
+
+// --- fail_todo_nested_in_friend_of_base.carbon
+library "[[@TEST_NAME]]";
+
+class Derived;
+
+base class Base {
+  friend Derived;
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+
+  class Inner {
+    fn ViaBase(b: Base) {
+      b.F();
+    }
+    fn ViaDerived(d: Derived) {
+      // CHECK:STDERR:        ╭─┤ fail_todo_nested_in_friend_of_base.carbon:[[@LINE+11]]:7
+      // CHECK:STDERR:        │   private fn F() {}
+      // CHECK:STDERR:        ·   ────────┬───────
+      // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+      // CHECK:STDERR:        ┆
+      // CHECK:STDERR: ->     │       d.F();
+      // CHECK:STDERR:        ·       ━┳━
+      // CHECK:STDERR:        ·        ┗━━┫ error: cannot access private member `F` of type `Base`
+      // CHECK:STDERR:        ·           ┃        [ClassInvalidMemberAccess]
+      // CHECK:STDERR:        ╰────
+      // CHECK:STDERR:
+      d.F();
+    }
+  }
+}
+
+// --- fail_todo_friend_of_base_via_template.carbon
+library "[[@TEST_NAME]]";
+
+class A(template T: type);
+
+base class Base {
+  friend A;
+  private fn F() {}
+}
+
+class A(template T: type) {
+  fn G() {
+    T.F();
+  }
+}
+
+class Derived {
+  extend base: Base;
+}
+
+fn H() {
+  // CHECK:STDERR:        ╭─┤ fail_todo_friend_of_base_via_template.carbon:[[@LINE+16]]:3
+  // CHECK:STDERR:        │   private fn F() {}
+  // CHECK:STDERR:        ·   ────────┬───────
+  // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+  // CHECK:STDERR:        ┆
+  // CHECK:STDERR:        │     T.F();
+  // CHECK:STDERR:        ·     ─┬─
+  // CHECK:STDERR:        ·      ╰──┤ cannot access private member `F` of type `Base`
+  // CHECK:STDERR:        ·         │ [ClassInvalidMemberAccess]
+  // CHECK:STDERR:        ┆
+  // CHECK:STDERR: ->     │   A(Derived).G();
+  // CHECK:STDERR:        ·   ━━━━━━┳━━━━━
+  // CHECK:STDERR:        ·         ┗━━┫ error: unable to monomorphize specific `G()`
+  // CHECK:STDERR:        ·            ┃        [ResolvingSpecificHere]
+  // CHECK:STDERR:        ╰────
+  // CHECK:STDERR:
+  A(Derived).G();
+}
+
+// --- fail_todo_base_member_via_derived.carbon
+library "[[@TEST_NAME]]";
+
+class Derived;
+
+base class Base {
+  private fn F() {}
+  fn G(d: Derived);
+}
+
+class Derived {
+  extend base: Base;
+}
+
+fn Base.G(d: Derived) {
+  // CHECK:STDERR:        ╭─┤ fail_todo_base_member_via_derived.carbon:[[@LINE+11]]:3
+  // CHECK:STDERR:        │   private fn F() {}
+  // CHECK:STDERR:        ·   ────────┬───────
+  // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+  // CHECK:STDERR:        ┆
+  // CHECK:STDERR: ->     │   d.F();
+  // CHECK:STDERR:        ·   ━┳━
+  // CHECK:STDERR:        ·    ┗━━┫ error: cannot access private member `F` of type `Base`
+  // CHECK:STDERR:        ·       ┃        [ClassInvalidMemberAccess]
+  // CHECK:STDERR:        ╰────
+  // CHECK:STDERR:
+  d.F();
+}
+
+// --- fail_todo_generic_base_member_via_derived.carbon
+library "[[@TEST_NAME]]";
+
+class Derived;
+
+base class Base(T: type) {
+  private fn F() {}
+  fn G(d: Derived);
+}
+
+class Derived {
+  extend base: Base(());
+}
+
+fn Base(T: type).G(d: Derived) {
+  // CHECK:STDERR:        ╭─┤ fail_todo_generic_base_member_via_derived.carbon:[[@LINE+11]]:3
+  // CHECK:STDERR:        │   private fn F() {}
+  // CHECK:STDERR:        ·   ────────┬───────
+  // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+  // CHECK:STDERR:        ┆
+  // CHECK:STDERR: ->     │   d.F();
+  // CHECK:STDERR:        ·   ━┳━
+  // CHECK:STDERR:        ·    ┗━━┫ error: cannot access private member `F` of type `Base(())`
+  // CHECK:STDERR:        ·       ┃        [ClassInvalidMemberAccess]
+  // CHECK:STDERR:        ╰────
+  // CHECK:STDERR:
+  d.F();
+  T;
+}
+
+// --- fail_todo_generic_base_member_via_derived_in_nested_class.carbon
+library "[[@TEST_NAME]]";
+
+class Derived;
+
+base class Base(T: type) {
+  private fn F() {}
+
+  class Nested {
+    fn G(d: Derived);
+  }
+}
+
+class Derived {
+  extend base: Base(());
+}
+
+fn Base(T: type).Nested.G(d: Derived) {
+  // CHECK:STDERR:        ╭─┤ fail_todo_generic_base_member_via_derived_in_nested_class.carbon:[[@LINE+11]]:3
+  // CHECK:STDERR:        │   private fn F() {}
+  // CHECK:STDERR:        ·   ────────┬───────
+  // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+  // CHECK:STDERR:        ┆
+  // CHECK:STDERR: ->     │   d.F();
+  // CHECK:STDERR:        ·   ━┳━
+  // CHECK:STDERR:        ·    ┗━━┫ error: cannot access private member `F` of type `Base(())`
+  // CHECK:STDERR:        ·       ┃        [ClassInvalidMemberAccess]
+  // CHECK:STDERR:        ╰────
+  // CHECK:STDERR:
+  d.F();
+  T;
+}
+
+// --- fail_todo_friend_of_indirect_base.carbon
+library "[[@TEST_NAME]]";
+
+class Friend;
+
+base class Top {
+  friend Friend;
+  private fn F() {}
+}
+
+base class Middle {
+  extend base: Top;
+}
+
+class Bottom {
+  extend base: Middle;
+}
+
+class Friend {
+  fn G(b: Bottom) {
+    // CHECK:STDERR:        ╭─┤ fail_todo_friend_of_indirect_base.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     b.F();
+    // CHECK:STDERR:        ·     ━┳━
+    // CHECK:STDERR:        ·      ┗━━┫ error: cannot access private member `F` of type `Middle`
+    // CHECK:STDERR:        ·         ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    b.F();
+  }
+}
+
+// --- fail_todo_friend_interface_of_base.carbon
+library "[[@TEST_NAME]]";
+
+interface I;
+
+base class Base {
+  friend I;
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+}
+
+interface I {
+  default fn G(d: Derived) {
+    // CHECK:STDERR:        ╭─┤ fail_todo_friend_interface_of_base.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     d.F();
+    // CHECK:STDERR:        ·     ━┳━
+    // CHECK:STDERR:        ·      ┗━━┫ error: cannot access private member `F` of type `Base`
+    // CHECK:STDERR:        ·         ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    d.F();
+  }
+}
+
+// --- fail_todo_friend_of_adapted_class.carbon
+library "[[@TEST_NAME]]";
+
+class Adapter;
+
+class Adapted {
+  friend Adapter;
+  private fn F() {}
+}
+
+class Adapter {
+  extend adapt Adapted;
+
+  fn G() {
+    // CHECK:STDERR:        ╭─┤ fail_todo_friend_of_adapted_class.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     Self.F();
+    // CHECK:STDERR:        ·     ━━━┳━━
+    // CHECK:STDERR:        ·        ┗━━┫ error: cannot access private member `F` of type `Adapted`
+    // CHECK:STDERR:        ·           ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    Self.F();
+  }
+}
+
+// --- protected_via_indirect_base.carbon
+library "[[@TEST_NAME]]";
+
+base class Top {
+  protected fn F() {}
+}
+
+base class Middle {
+  extend base: Top;
+}
+
+class Bottom {
+  extend base: Middle;
+
+  fn G(self) {
+    self.F();
+  }
+}
+
+// --- private_member_shadows_indirect_base_member.carbon
+library "[[@TEST_NAME]]";
+
+class Friend;
+
+base class Top {
+  fn F() {}
+}
+
+base class Base {
+  extend base: Top;
+  friend Friend;
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+}
+
+class Friend {
+  fn G(d: Derived) {
+    d.F();
+  }
+}
+
+fn NonFriend(d: Derived) {
+  d.F();
+}
+
+// --- todo_fail_friend_of_base_ambiguous_with_extended_impl.carbon
+library "[[@TEST_NAME]]";
+
+class Friend;
+
+interface I {
+  fn F();
+}
+
+base class Base {
+  friend Friend;
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+  extend impl as I {
+    fn F() {}
+  }
+}
+
+class Friend {
+  fn G() {
+    // TODO: should fail, a friend of `Base` can see `Base.F`, so `F` is
+    // ambiguous between it and `I.F`.
+    Derived.F();
+  }
+}
+
+fn NonFriend() {
+  // Other code can't see `Base.F`, so finds only `I.F`.
+  Derived.F();
+}
+
+// --- fail_todo_friend_of_base_protected_member_of_indirect_base.carbon
+library "[[@TEST_NAME]]";
+
+class Friend;
+
+base class Top {
+  protected fn F() {}
+}
+
+base class Middle {
+  extend base: Top;
+  friend Friend;
+}
+
+class Bottom {
+  extend base: Middle;
+}
+
+class Friend {
+  fn G(m: Middle, b: Bottom) {
+    m.F();
+    // CHECK:STDERR:        ╭─┤ fail_todo_friend_of_base_protected_member_of_indirect_base.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   protected fn F() {}
+    // CHECK:STDERR:        ·   ─────────┬────────
+    // CHECK:STDERR:        ·            ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     b.F();
+    // CHECK:STDERR:        ·     ━┳━
+    // CHECK:STDERR:        ·      ┗━━┫ error: cannot access protected member `F` of type `Bottom`
+    // CHECK:STDERR:        ·         ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    b.F();
+  }
+}
+
+// --- fail_not_friend_of_base.carbon
+library "[[@TEST_NAME]]";
+
+class Derived;
+
+base class Base {
+  friend Derived;
+  private fn F();
+}
+
+class Derived {
+  extend base: Base;
+}
+
+fn G(d: Derived) {
+  // CHECK:STDERR:        ╭─┤ fail_not_friend_of_base.carbon:[[@LINE+11]]:3
+  // CHECK:STDERR:        │   private fn F();
+  // CHECK:STDERR:        ·   ───────┬───────
+  // CHECK:STDERR:        ·          ╰──┤ declared here [ClassMemberDeclaration]
+  // CHECK:STDERR:        ┆
+  // CHECK:STDERR: ->     │   d.F();
+  // CHECK:STDERR:        ·   ━┳━
+  // CHECK:STDERR:        ·    ┗━━┫ error: cannot access private member `F` of type `Base`
+  // CHECK:STDERR:        ·       ┃        [ClassInvalidMemberAccess]
+  // CHECK:STDERR:        ╰────
+  // CHECK:STDERR:
+  d.F();
+}
+
+// --- fail_friend_of_derived_only.carbon
+library "[[@TEST_NAME]]";
+
+class Friend;
+
+base class Base {
+  private fn F();
+}
+
+class Derived {
+  extend base: Base;
+  friend Friend;
+  private fn G();
+}
+
+class Friend {
+  fn H(d: Derived) {
+    d.G();
+    // CHECK:STDERR:        ╭─┤ fail_friend_of_derived_only.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F();
+    // CHECK:STDERR:        ·   ───────┬───────
+    // CHECK:STDERR:        ·          ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     d.F();
+    // CHECK:STDERR:        ·     ━┳━
+    // CHECK:STDERR:        ·      ┗━━┫ error: cannot access private member `F` of type `Base`
+    // CHECK:STDERR:        ·         ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    d.F();
+  }
+}
+
+// --- fail_derived_without_friendship_qualified.carbon
+library "[[@TEST_NAME]]";
+
+base class Base {
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+
+  fn Qualified() {
+    // CHECK:STDERR:        ╭─┤ fail_derived_without_friendship_qualified.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     Self.F();
+    // CHECK:STDERR:        ·     ━━━┳━━
+    // CHECK:STDERR:        ·        ┗━━┫ error: cannot access private member `F` of type `Base`
+    // CHECK:STDERR:        ·           ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    Self.F();
+  }
+}
+
+// --- fail_derived_without_friendship_unqualified.carbon
+library "[[@TEST_NAME]]";
+
+base class Base {
+  private fn F() {}
+}
+
+class Derived {
+  extend base: Base;
+
+  fn Unqualified() {
+    // CHECK:STDERR:        ╭─┤ fail_derived_without_friendship_unqualified.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     F();
+    // CHECK:STDERR:        ·     ┳
+    // CHECK:STDERR:        ·     ┗━━┫ error: cannot access private member `F` of type `Base`
+    // CHECK:STDERR:        ·        ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    F();
+  }
+}
+
+// --- fail_friend_of_middle_only.carbon
+library "[[@TEST_NAME]]";
+
+class Friend;
+
+base class Top {
+  private fn F();
+}
+
+base class Middle {
+  extend base: Top;
+  friend Friend;
+}
+
+class Bottom {
+  extend base: Middle;
+}
+
+class Friend {
+  fn G(b: Bottom) {
+    // CHECK:STDERR:        ╭─┤ fail_friend_of_middle_only.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F();
+    // CHECK:STDERR:        ·   ───────┬───────
+    // CHECK:STDERR:        ·          ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     b.F();
+    // CHECK:STDERR:        ·     ━┳━
+    // CHECK:STDERR:        ·      ┗━━┫ error: cannot access private member `F` of type `Middle`
+    // CHECK:STDERR:        ·         ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    b.F();
+  }
+}
+
+// --- fail_not_friend_of_adapted_class.carbon
+library "[[@TEST_NAME]]";
+
+class Adapted {
+  private fn F() {}
+}
+
+class Adapter {
+  extend adapt Adapted;
+
+  fn G() {
+    // CHECK:STDERR:        ╭─┤ fail_not_friend_of_adapted_class.carbon:[[@LINE+11]]:5
+    // CHECK:STDERR:        │   private fn F() {}
+    // CHECK:STDERR:        ·   ────────┬───────
+    // CHECK:STDERR:        ·           ╰──┤ declared here [ClassMemberDeclaration]
+    // CHECK:STDERR:        ┆
+    // CHECK:STDERR: ->     │     Self.F();
+    // CHECK:STDERR:        ·     ━━━┳━━
+    // CHECK:STDERR:        ·        ┗━━┫ error: cannot access private member `F` of type `Adapted`
+    // CHECK:STDERR:        ·           ┃        [ClassInvalidMemberAccess]
+    // CHECK:STDERR:        ╰────
+    // CHECK:STDERR:
+    Self.F();
+  }
+}