# Building Project with Depedencies' Tests: CMake FetchContent Conflicting Targets

**URL:** https://discourse.cmake.org/t/building-project-with-depedencies-tests-cmake-fetchcontent-conflicting-targets/9747
**Category:** Usage
**Created:** [December 31, 2023, 12:03pm UTC](https://discourse.cmake.org/t/building-project-with-depedencies-tests-cmake-fetchcontent-conflicting-targets/9747 "2023-12-31T12:03:35Z")
**Posts on this page:** 3
**Page:** 1

<div class="post-metadata">

### Author: ![eulersson](https://discourse.cmake.org/user_avatar/discourse.cmake.org/eulersson/32/4126_2.png) [@eulersson](https://discourse.cmake.org/u/eulersson)
#### Post date: [December 31, 2023, 12:03pm UTC](https://discourse.cmake.org/t/building-project-with-depedencies-tests-cmake-fetchcontent-conflicting-targets/9747/1 "2023-12-31T12:03:35Z")

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Hello, I have problems building a project with two external dependencies that define the same target.

My goal is to be able to compile the project’s tests along with the project’s dependencies  
tests too. For that I was thinking of building the unit tests when compiling from source  
with FetchContent. If you included `include(CTest)` any subsequent calls to add\_test would  
include that test so afterwards all the tests (project + dependencies’) can be run with  
`ctest` on on the build dir (`ctest --test-dir build`):

```auto
$ ctest --test-dir build
Internal ctest changing into directory: /home/eulersson/cmake-fetchcontent-conflicting-targets/build
Test project /home/eulersson/cmake-fetchcontent-conflicting-targets/build
(FIRST IT RUNS THE TESTS FROM THIS PROJECT (TEST_FOO))
      Start 1: test-foo
 1/62 Test #1: test-foo .......................... Passed 0.02 sec
 (NOW IT WOULD RUN THE TESTS FROM CJSON (DEPENDENCY))
      Start 2: cJSON_test
 2/62 Test #2: cJSON_test ........................ Passed 0.02 sec
      Start 3: parse_examples
[...]
 (NOW IT WOULD RUN THE TESTS FROM LIBZMQ (DEPENDENCY))
[...]

```

Does this make sense? Perhaps there’s another way that conform to best practices?

When adding various dependencies into a CMake project, if you want to also build the  
unit tests along them, I run into this problem where the target (in this case the unit  
testing library “unity”) is being added twice by the various dependencies you want to  
build tests for (add\_library(unity STATIC […])):

- add\_library(unity […]) in `libzmq: https://github.com/zeromq/libzmq/blob/959a133520dfc80d29e83aa7ef762e1d0327f63b/tests/CMakeLists.txt#L206-L209`
- add\_library(unity […]) in cJSON: `https://github.com/DaveGamble/cJSON/blob/19ff92da79ee37c81a4cdf1f50a8dd1cbb02e84f/tests/CMakeLists.txt#L2`

Reproducible exampe: GitHub - eulersson/cmake-fetchcontent-conflicting-targets: Problem illustrating using FetchContent on projects defining the same un-namespaced target.

```auto
$ git clone https://github.com/eulersson/cmake-conflicting-targets
$ cd cmake-conflicting-targets
$ cmake -S . -B build
[...]
CMake Error at build/_deps/cjson-src/tests/CMakeLists.txt:2 (add_library):
  add_library cannot create target "unity" because another target with the
  same name already exists. The existing target is a static library created
  in source directory
  "/Users/ramon/Devel/conflicting-targets/build/_deps/libzmq-src/tests". See
  documentation for policy CMP0002 for more details.

```

This would not be an issue if those targets were namespaced.

What would be a good workaround?

Thanks in advance.

---

<div class="post-metadata">

### Author: ![ben.boeckel](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/b/ea5d25/32.png) [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [January 11, 2024, 2:15pm UTC](https://discourse.cmake.org/t/building-project-with-depedencies-tests-cmake-fetchcontent-conflicting-targets/9747/2 "2024-01-11T14:15:09Z")

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There’s not a good workaround; vendoring is not a mechanical transformation and these kinds of conflicts can happen all over the place. It’s just something that vendoring needs to deal with.

@craig.scott does have a proposal for adding a `NAMESPACE` argument to `add_subdirectory` for some level of assistance for vendoring but I have no insight into any progress there.

---

<div class="post-metadata">

### Author: ![craig.scott](https://discourse.cmake.org/user_avatar/discourse.cmake.org/craig.scott/32/20_2.png) [@craig.scott](https://discourse.cmake.org/u/craig.scott)
#### Post date: [January 12, 2024, 8:40am UTC](https://discourse.cmake.org/t/building-project-with-depedencies-tests-cmake-fetchcontent-conflicting-targets/9747/3 "2024-01-12T08:40:41Z")

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This is the proposal for project namespaces (it’s not about `add_subdirectory()`, it’s more about `project()`): [https://gitlab.kitware.com/cmake/cmake/-/issues/22687](https://gitlab.kitware.com/cmake/cmake/-/issues/22687)

There’s no progress on that beyond the discussion in that issue. I don’t expect to be working on it any time soon, if at all given current commitments and my growing TODO list. It’s a big chunk of work that will require a sustained effort to complete.