diff --git a/clang-tools-extra/test/clang-tidy/check_clang_tidy.py b/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
--- a/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
+++ b/clang-tools-extra/test/clang-tidy/check_clang_tidy.py
@@ -265,15 +265,17 @@
 
 def expand_std(std):
     if std == "c++98-or-later":
-        return ["c++98", "c++11", "c++14", "c++17", "c++20"]
+        return ["c++98", "c++11", "c++14", "c++17", "c++20", "c++23", "c++2c"]
     if std == "c++11-or-later":
-        return ["c++11", "c++14", "c++17", "c++20"]
+        return ["c++11", "c++14", "c++17", "c++20", "c++23", "c++2c"]
     if std == "c++14-or-later":
-        return ["c++14", "c++17", "c++20"]
+        return ["c++14", "c++17", "c++20", "c++23", "c++2c"]
     if std == "c++17-or-later":
-        return ["c++17", "c++20"]
+        return ["c++17", "c++20", "c++23", "c++2c"]
     if std == "c++20-or-later":
-        return ["c++20"]
+        return ["c++20", "c++23", "c++2c"]
+    if std == "c++23-or-later":
+        return ["c++23", "c++2c"]
     return [std]
 
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-values-before-cxx23.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-values-before-cxx23.cpp
new file mode 100644
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-values-before-cxx23.cpp
@@ -0,0 +1,20 @@
+// RUN: %check_clang_tidy -std=c++11,c++14,c++17,c++20 %s misc-const-correctness %t -- \
+// RUN:   -config="{CheckOptions: {\
+// RUN:     misc-const-correctness.TransformValues: true, \
+// RUN:     misc-const-correctness.WarnPointersAsValues: false, \
+// RUN:     misc-const-correctness.TransformPointersAsValues: false \
+// RUN:   }}" -- -fno-delayed-template-parsing
+
+
+double &non_const_ref_return() {
+  double p_local0 = 0.0;
+  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: variable 'p_local0' of type 'double' can be declared 'const'
+  // CHECK-FIXES: double const p_local0
+  double np_local0 = 42.42;
+  return np_local0;
+}
+
+double *&return_non_const_pointer_ref() {
+  double *np_local0 = nullptr;
+  return np_local0;
+}
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-values.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-values.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-values.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc/const-correctness-values.cpp
@@ -1,9 +1,9 @@
 // RUN: %check_clang_tidy %s misc-const-correctness %t -- \
 // RUN:   -config="{CheckOptions: {\
-// RUN:   misc-const-correctness.TransformValues: true, \
-// RUN:   misc-const-correctness.WarnPointersAsValues: false, \
-// RUN:   misc-const-correctness.TransformPointersAsValues: false} \
-// RUN:   }" -- -fno-delayed-template-parsing
+// RUN:     misc-const-correctness.TransformValues: true, \
+// RUN:     misc-const-correctness.WarnPointersAsValues: false, \
+// RUN:     misc-const-correctness.TransformPointersAsValues: false \
+// RUN:   }}" -- -fno-delayed-template-parsing
 
 // ------- Provide test samples for primitive builtins ---------
 // - every 'p_*' variable is a 'potential_const_*' variable
@@ -181,14 +181,7 @@
   return &p_local1;
 }
 
-double &non_const_ref_return() {
-  double p_local0 = 0.0;
-  // CHECK-MESSAGES: [[@LINE-1]]:3: warning: variable 'p_local0' of type 'double' can be declared 'const'
-  // CHECK-FIXES: double const p_local0
-  double np_local0 = 42.42;
-  return np_local0;
-}
-
+// Also see const-correctness-values.cpp-before-cxx23.cpp for `non_const_ref_return` and `return_non_const_pointer_ref`
 const double &const_ref_return() {
   double p_local0 = 0.0;
   // CHECK-MESSAGES: [[@LINE-1]]:3: warning: variable 'p_local0' of type 'double' can be declared 'const'
@@ -199,11 +192,6 @@
   return p_local1;
 }
 
-double *&return_non_const_pointer_ref() {
-  double *np_local0 = nullptr;
-  return np_local0;
-}
-
 void overloaded_arguments(const int &in);
 void overloaded_arguments(int &inout);
 void overloaded_arguments(const int *in);
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc/unconventional-assign-operator.cpp
@@ -45,7 +45,7 @@
   BadArgument& operator=(BadArgument&);
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should take 'BadArgument const&', 'BadArgument&&' or 'BadArgument'
   BadArgument& operator=(const BadArgument&&);
-  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should take 'BadAr
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: operator=() should take 'BadArgument const&', 'BadArgument&&' or 'BadArgument'
 };
 
 struct BadModifier {
@@ -76,7 +76,7 @@
 public:
   BadReturnStatement& operator=(BadReturnStatement&& rhs) {
     n = std::move(rhs.n);
-    return rhs;
+    return *&rhs;
 // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: operator=() should always return '*this'
   }
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability/container-contains.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability/container-contains.cpp
--- a/clang-tools-extra/test/clang-tidy/checkers/readability/container-contains.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability/container-contains.cpp
@@ -1,4 +1,4 @@
-// RUN: %check_clang_tidy -std=c++20 %s readability-container-contains %t
+// RUN: %check_clang_tidy -std=c++20-or-later %s readability-container-contains %t
 
 // Some *very* simplified versions of `map` etc.
 namespace std {