Start CMake modernization scaffold

tests/test_harness.h

@@ -0,0 +1,50 @@
+#pragma once
+
+#include <cstdlib>
+#include <iostream>
+#include <string_view>
+
+namespace pp::tests {
+
+class Harness {
+public:
+    void expect(bool condition, std::string_view expression, std::string_view file, int line)
+    {
+        ++assertions_;
+        if (!condition) {
+            ++failures_;
+            std::cerr << file << ":" << line << ": expectation failed: " << expression << "\n";
+        }
+    }
+
+    template <typename Callback>
+    void run(std::string_view name, Callback callback)
+    {
+        const auto failures_before = failures_;
+        callback(*this);
+        ++tests_;
+        if (failures_ == failures_before) {
+            std::cout << "[pass] " << name << "\n";
+        } else {
+            std::cout << "[fail] " << name << "\n";
+        }
+    }
+
+    [[nodiscard]] int finish() const
+    {
+        std::cout << "{\"tests\":" << tests_
+                  << ",\"assertions\":" << assertions_
+                  << ",\"failures\":" << failures_ << "}\n";
+        return failures_ == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
+    }
+
+private:
+    int tests_ = 0;
+    int assertions_ = 0;
+    int failures_ = 0;
+};
+
+}
+
+#define PP_EXPECT(harness, expression) \
+    (harness).expect(static_cast<bool>(expression), #expression, __FILE__, __LINE__)