tests: Use MakeUnique to construct objects owned by unique_ptrs

doc/developer-notes.md

@@ -439,6 +439,11 @@ General C++
 
   - *Rationale*: This avoids memory and resource leaks, and ensures exception safety
 
+- Use `MakeUnique()` to construct objects owned by `unique_ptr`s
+
+  - *Rationale*: `MakeUnique` is concise and ensures exception safety in complex expressions.
+    `MakeUnique` is a temporary project local implementation of `std::make_unique` (C++14).
+
 C++ data structures
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