feat: provide and use a common calling interface to all chapter tests

chapters/chapter_02/include/constexp.h

@@ -1,5 +1,8 @@
 #pragma once
 
-namespace constexp {
-void test();
+#include "chapter_interface.h"
+
+class ConstExpTest : public ChapterTest {
+public:
+  virtual void test() override;
 };

chapters/chapter_02/include/ifswitch.h

@@ -1,7 +1,8 @@
 #pragma once
 
-namespace ifswitch {
-
-void test();
+#include "chapter_interface.h"
 
+class IfswitchTest : public ChapterTest {
+public:
+  virtual void test() override;
 };

chapters/chapter_02/include/initlist.h

@@ -1,5 +1,8 @@
 #pragma once
 
-namespace initlist {
-void test();
+#include "chapter_interface.h"
+
+class InitListTest : public ChapterTest {
+public:
+  virtual void test() override;
 };

chapters/chapter_02/include/null.h

@@ -1,5 +1,8 @@
 #pragma once
 
-namespace null {
-void test();
+#include "chapter_interface.h"
+
+class NullTest : public ChapterTest {
+public:
+  virtual void test() override;
 };