I completely agree with you. The lack of a module system (still missing in C++17) and of standard libraries that are commonplace in other languages (testing, string formatting...) are the two most serious drawbacks which are preventing me from using C++ anymore.
The fact that there is a nice subset of C++ which works well is not a valid argument, in practice. As you say, you are forced to include in your projects a lot of libraries, each assuming its own definition of what this subset is, and the union of those subsets can be a monster.
You can grab Catch as a test framework. It's a single header file you can include directly in your directory and it takes like 2 minutes to learn how to use.
Thanks, I didn't know about Catch. However, my point is that this kind of tools should be part of the standard library, like it's the case for other modern languages.
The fact that there is a nice subset of C++ which works well is not a valid argument, in practice. As you say, you are forced to include in your projects a lot of libraries, each assuming its own definition of what this subset is, and the union of those subsets can be a monster.