diff --git a/.github/workflows/ci_documentation.yml b/.github/workflows/ci_documentation.yml
index 82e5395..6c2be7c 100644
--- a/.github/workflows/ci_documentation.yml
+++ b/.github/workflows/ci_documentation.yml
@@ -51,8 +51,6 @@ jobs:
         run: |
           mkdir build && cd build
           cmake .. -DCMAKE_BUILD_TYPE=Release \
-                   -Dneedle_TEST=OFF \
-                   -Dneedle_DOCS=ON \
                    -DNEEDLE_TEST=OFF \
                    -DNEEDLE_DOCS=ON
 
diff --git a/.github/workflows/ci_install.yml b/.github/workflows/ci_install.yml
index e13d5bd..4d223d8 100644
--- a/.github/workflows/ci_install.yml
+++ b/.github/workflows/ci_install.yml
@@ -44,33 +44,59 @@ jobs:
         with:
           path: needle
 
+      - name: Remove ccache
+        run: apt-get purge --yes ccache
+
       - name: Create source package
         run: |
-          mkdir package && cd package
+          mkdir create_source_package && cd create_source_package
           cmake ../needle -DCMAKE_BUILD_TYPE=Release \
-                          -Dneedle_PACKAGE=ON \
-                          -Dneedle_TEST=OFF
+                          -DNEEDLE_PACKAGE=ON \
+                          -DNEEDLE_TEST=OFF
           make package_source
-          mkdir ../unpacked
-          tar xf needle-*.tar.xz -C ../unpacked --strip-components=1
+          mkdir ../source_package
+          tar xf needle-*.tar.xz -C ../source_package --strip-components=1
 
       - name: Install from source package
+        run: |
+          mkdir build_from_source_package install && cd build_from_source_package
+          unshare -r -n cmake ../source_package -DCMAKE_BUILD_TYPE=Release \
+                                                -DCMAKE_INSTALL_PREFIX=${GITHUB_WORKSPACE}/install \
+                                                -DNEEDLE_TEST=OFF
+          unshare -r -n make install
+
+      - name: Check installed executable
+        run: ${GITHUB_WORKSPACE}/install/bin/needle --help
+
+      # Clang builds with libc++, but GTest is built with libstdc++
+      - name: Install GTest
+        if: contains(matrix.compiler, 'gcc')
+        run: apt-get update && apt-get install --yes libgtest-dev
+
+      - name: Build tests
+        if: contains(matrix.compiler, 'gcc')
         run: |
           mkdir build && cd build
-          unshare -r -n cmake ../unpacked -DCMAKE_BUILD_TYPE=Release \
-                                          -DCMAKE_INSTALL_PREFIX=$(pwd)/install \
-                                          -Dneedle_TEST=OFF
-          make install
+          unshare -r -n  cmake ../source_package -DCMAKE_BUILD_TYPE=Release \
+                                                 -DCPM_USE_LOCAL_PACKAGES=ON \
+                                                 -DNEEDLE_TEST_BINARY_DIR=${GITHUB_WORKSPACE}/install/bin \
+                                                 -DNEEDLE_TEST=ON
+          unshare -r -n make -k tests
+          test -n $(find . -type f -executable -name "needle") # needle binary should exist
+          rm bin/needle
+          test -z $(find . -type f -executable -name "needle") # needle binary should not exist
 
       - name: Run tests
+        if: contains(matrix.compiler, 'gcc')
         working-directory: build
-        run: ./install/bin/needle --help
+        run: |
+          unshare -r -n ctest -j --output-on-failure --test-dir test
+          test -z $(find . -type f -executable -name "needle") # needle binary should not exist
 
       - name: Upload source package
-        if: matrix.compiler == 'gcc-14'
+        if: contains(matrix.compiler, 'gcc')
         uses: actions/upload-artifact@v4
         with:
-          name: source-package
-          path: package/needle-*.tar.xz*
+          name: needle-source-package
+          path: create_source_package/needle-*.tar.xz*
           retention-days: 1
-
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 025244b..bf48362 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,11 +22,11 @@ include (output_directories)
 # It can be used when calling CMake: `cmake .. -Dapp-template_TEST=OFF`.
 # It is good practice to allow disabling tests. If another project includes your application,
 # it might not want to build your tests.
-option (${PROJECT_NAME}_TEST "Enable testing for ${PROJECT_NAME}." ON)
-option (${PROJECT_NAME}_DOCS "Enable documentation for ${PROJECT_NAME}." OFF)
-option (${PROJECT_NAME}_PACKAGE "Enable packaging for ${PROJECT_NAME}." OFF)
+option (NEEDLE_TEST "Enable testing for NEEDLE." ON)
+option (NEEDLE_DOCS "Enable documentation for NEEDLE." OFF)
+option (NEEDLE_PACKAGE "Enable packaging for NEEDLE." OFF)
 
-if (${PROJECT_NAME}_PACKAGE)
+if (NEEDLE_PACKAGE)
     set (CPM_SOURCE_CACHE "${CMAKE_CURRENT_BINARY_DIR}/vendor")
     set (CPM_USE_LOCAL_PACKAGES OFF)
     include (package)
@@ -48,11 +48,11 @@ CPMGetPackage (robin-hood)
 # Add the application. This will include `src/CMakeLists.txt`.
 add_subdirectory (src)
 
-if (${PROJECT_NAME}_TEST)
+if (NEEDLE_TEST)
     # Add the tests. This will include `test/CMakeLists.txt`.
     add_subdirectory (test EXCLUDE_FROM_ALL)
 endif ()
 
-if (${PROJECT_NAME}_DOCS)
+if (NEEDLE_DOCS)
     add_subdirectory (doc EXCLUDE_FROM_ALL)
 endif ()
diff --git a/cmake/test/config.cmake b/cmake/test/config.cmake
index e99e2a8..ce56b72 100644
--- a/cmake/test/config.cmake
+++ b/cmake/test/config.cmake
@@ -13,9 +13,21 @@ enable_testing ()
 file (MAKE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/output)
 add_definitions (-DOUTPUTDIR=\"${CMAKE_CURRENT_BINARY_DIR}/output/\")
 add_definitions (-DDATADIR=\"${CMAKE_CURRENT_BINARY_DIR}/data/\")
-add_definitions (-DBINDIR=\"${CMAKE_BINARY_DIR}/bin/\")
 add_definitions (-DAPPNAME=\"${PROJECT_NAME}\")
 
+if (NEEDLE_TEST_BINARY_DIR)
+    if (NOT EXISTS "${NEEDLE_TEST_BINARY_DIR}")
+        message (FATAL_ERROR "The directory \"${NEEDLE_TEST_BINARY_DIR}\" (NEEDLE_TEST_BINARY_DIR) does not exist.")
+    endif ()
+    if (NOT EXISTS "${NEEDLE_TEST_BINARY_DIR}/${PROJECT_NAME}")
+        message (FATAL_ERROR "Executable \"${PROJECT_NAME}\" not found in \"${NEEDLE_TEST_BINARY_DIR}\" (NEEDLE_TEST_BINARY_DIR)."
+        )
+    endif ()
+else ()
+    set (NEEDLE_TEST_BINARY_DIR "${CMAKE_BINARY_DIR}/bin")
+endif ()
+add_definitions (-DBINDIR=\"${NEEDLE_TEST_BINARY_DIR}/\")
+
 # Add the test interface library.
 if (NOT TARGET ${PROJECT_NAME}_test)
     add_library (${PROJECT_NAME}_test INTERFACE)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 18acf8c..a9f06d2 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -18,17 +18,8 @@ set_target_properties ("${PROJECT_NAME}" PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${
 include (GNUInstallDirs)
 install (TARGETS ${PROJECT_NAME} RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}")
 
-# https://cmake.org/cmake/help/latest/module/CMakeDependentOption.html
-# We usually want "-Werror" in the CI, but not when developing locally.
-# Virtually all CI providers set the environment variable `CI` to some value.
-# If `CI` is defined in the environment, we use `-Werror`, otherwise not.
-# Caveat: If `CI` is not set, `-Dneedle_WITH_WERROR=ON` has no effect.
-#         The other way around works. If `CI` is set, `-Dneedle_WITH_WERROR=OFF` is honored.
-# Solutions: * `export CI=1` (any value after `=` works, the variable only needs to be not empty)
-#            * `-DCMAKE_CXX_FLAGS="-Werror"`
-include (CMakeDependentOption)
-cmake_dependent_option (${PROJECT_NAME}_WITH_WERROR "Report compiler warnings as errors." ON "DEFINED ENV{CI}" OFF)
+option (NEEDLE_WITH_WERROR "Report compiler warnings as errors." ON)
 
-if (${PROJECT_NAME}_WITH_WERROR)
+if (NEEDLE_WITH_WERROR)
     target_compile_options (${PROJECT_NAME}_lib PUBLIC "-Werror")
 endif ()