Normalize C++ namespace in JUnit's reporter classname field

Closes #2468

tests/CMakeLists.txt

@@ -553,6 +553,17 @@ set_tests_properties("Colours::ColourModeCanBeExplicitlySetToAnsi"
     PASS_REGULAR_EXPRESSION "\\[1\;32mAll tests passed"
 )
 
+add_test(NAME "Reporters::JUnit::NamespacesAreNormalized"
+  COMMAND
+    $<TARGET_FILE:SelfTest>
+      --reporter junit
+      "A TEST_CASE_METHOD testing junit classname normalization"
+)
+set_tests_properties("Reporters::JUnit::NamespacesAreNormalized"
+  PROPERTIES
+    PASS_REGULAR_EXPRESSION "testcase classname=\"SelfTest(\.exe)?\\.A\\.B\\.TestClass\""
+)
+
 if (CATCH_ENABLE_CONFIGURE_TESTS)
     foreach(testName "DefaultReporter" "Disable" "DisableStringification"
                      "ExperimentalRedirect")

tests/SelfTest/UsageTests/Class.tests.cpp

@@ -114,4 +114,20 @@ namespace Inner
     {
         REQUIRE(Template_Fixture_2<TestType>{}.m_a.size() < 2);
     }
+} // namespace
+
+
+// We want a class in nested namespace so we can test JUnit's classname normalization.
+namespace {
+    namespace A {
+        namespace B {
+            class TestClass {};
+        }
+    }
+} // namespace
+
+TEST_CASE_METHOD( A::B::TestClass,
+                  "A TEST_CASE_METHOD testing junit classname normalization",
+                  "[class][approvals]" ) {
+    SUCCEED();
 }