Move tests to separate directories, and document

Today, with the tests inside a `tests` intermingled with the
corresponding library's source code, we have a few problems:

- We have to be careful that wildcards don't end up with tests being
  built as part of Nix proper, or test headers being installed as part
  of Nix proper.

- Tests in libraries but not executables is not right:

  - It means each executable runs the previous unit tests again, because
    it needs the libraries.

  - It doesn't work right on Windows, which doesn't want you to load a
    DLL just for the side global variable . It could be made to work
    with the dlopen equivalent, but that's gross!

This reorg solves these problems.

There is a remaining problem which is that sibbling headers (like
`hash.hh` the test header vs `hash.hh` the main `libnixutil` header) end
up shadowing each other. This PR doesn't solve that. That is left as
future work for a future PR.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>

(cherry picked from commit 91b6833686a6a6d9eac7f3f66393ec89ef1d3b57)
(cherry picked from commit a61e42adb528b3d40ce43e07c79368d779a8b624)

1 files changed, 0 insertions, 31 deletions

diff --git a/src/libexpr/tests/value/context.hh b/src/libexpr/tests/value/context.hh
deleted file mode 100644
index c0bc97ba3..000000000
--- a/src/libexpr/tests/value/context.hh
+++ /dev/null
@@ -1,31 +0,0 @@
-#pragma once
-///@file
-
-#include <rapidcheck/gen/Arbitrary.h>
-
-#include <value/context.hh>
-
-namespace rc {
-using namespace nix;
-
-template<>
-struct Arbitrary<NixStringContextElem::Opaque> {
-    static Gen<NixStringContextElem::Opaque> arbitrary();
-};
-
-template<>
-struct Arbitrary<NixStringContextElem::Built> {
-    static Gen<NixStringContextElem::Built> arbitrary();
-};
-
-template<>
-struct Arbitrary<NixStringContextElem::DrvDeep> {
-    static Gen<NixStringContextElem::DrvDeep> arbitrary();
-};
-
-template<>
-struct Arbitrary<NixStringContextElem> {
-    static Gen<NixStringContextElem> arbitrary();
-};
-
-}