Added some actions for testing and install.

.github/workflows/check-install.yaml

@@ -0,0 +1,50 @@
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+name: Check CMake install
+
+jobs:
+  install:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Get latest CMake
+      uses: lukka/get-cmake@latest
+
+    - name: Install knncolle
+      run: |
+        git clone https://github.com/knncolle/knncolle dep-knncolle --depth=1
+        cd dep-knncolle
+        cmake -S . -B build -DKNNCOLLE_TESTS=OFF
+        sudo cmake --install build
+
+    - name: Install Annoy
+      run: |
+        git clone https://github.com/nmslib/hnswlib dep-hnsw --depth=1
+        cd dep-hnsw
+        cmake -S . -B build
+        sudo cmake --install build
+
+    - name: Configure the build
+      run: cmake -S . -B build -DKNNCOLLE_HNSW_TESTS=OFF -DKNNCOLLE_HNSW_FETCH_EXTERN=OFF
+
+    - name: Install the library
+      run: sudo cmake --install build
+
+    - name: Test downstream usage
+      run: |
+        mkdir _downstream
+        touch _downstream/source.cpp
+        cat << EOF > _downstream/CMakeLists.txt
+        cmake_minimum_required(VERSION 3.24)
+        project(test_install)
+        add_executable(whee source.cpp)
+        find_package(knncolle_knncolle_hnsw)
+        target_link_libraries(whee knncolle::knncolle_hnsw)
+        EOF
+        cd _downstream && cmake -S . -B build

.github/workflows/run-tests.yaml

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+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+name: Run unit tests
+
+jobs:
+  build:
+    name: ${{ matrix.config.name }}
+    runs-on: ${{ matrix.config.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        config:
+        - {
+            name: "Ubuntu Latest GCC, coverage enabled", 
+            os: ubuntu-latest,
+            cov: true
+          }
+        - {
+            name: "macOS Latest Clang", 
+            os: macos-latest,
+            cov: false
+          }
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Get latest CMake
+      uses: lukka/get-cmake@latest
+
+    - name: Configure the build
+      if: ${{ matrix.config.cov == false }}
+      run: cmake -S . -B build
+
+    - name: Configure the build with coverage
+      if: ${{ matrix.config.cov == true }}
+      run: cmake -S . -B build -DCODE_COVERAGE=ON
+
+    - name: Run the build
+      run: cmake --build build
+
+    - name: Run the tests
+      run: |
+        cd build
+        # Avoid using ctest because it's so slow; it starts a
+        # new process for each individual test, which is crazy.
+        for exe in $(ctest --show-only=json-v1 | jq -r ".tests[] | .command | .[0]"  | sort | uniq)
+        do
+            echo "#### RUNNING ${exe} ####"
+            echo 
+            ${exe} --gtest_brief=1
+            echo
+        done 
+
+    - name: Generate code coverage
+      if: ${{ matrix.config.cov == true }}
+      run: |
+        cd build/tests/CMakeFiles/libtest.dir/src/
+        gcov -abcfu *.gcno
+
+    - name: Upload to Codecov
+      if: ${{ matrix.config.cov == true }}
+      uses: codecov/codecov-action@v4
+      with:
+        directory: build/tests/CMakeFiles/libtest.dir/src/
+      env:
+        CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}