Test Native and GSL Implementations

classifier-reborn is designed to work with or without
[GSL](https://www.gnu.org/software/gsl/) support.

https://github.com/jekyll/classifier-reborn/blob/99d13af5adf040ba40a6fe77dbe0b28756562fcc/docs/index.md?plain=1#L68

If GSL is installed, classifier-reborn will detect it and use it. If GSL
is not installed, classifier-reborn will fall back to a pure-ruby
implementation. The mechanism for doing so is in `lsi.rb`:

https://github.com/jekyll/classifier-reborn/blob/99d13af5adf040ba40a6fe77dbe0b28756562fcc/lib/classifier-reborn/lsi.rb#L7-L17

Notably, there's a comment there about how to test with/without GSL
enabled.

> to test the native vector class, try `rake test NATIVE_VECTOR=true`

As far as I can tell, this was only ever used for local
development/testing, and was never tested in CI (though it was
previously discussed
[here](jekyll#46 (comment))).
I did not include this in my last PR (jekyll#195) because I was focused on
porting existing testing functionality from TravisCI to GitHub Actions.
Now that GitHub Actions is working, I think it's important to expand our
CI coverage to test with and without GSL in CI. So, in this PR, I'm
doing so by setting `NATIVE_VECTOR` to true or false in our test matrix.
Lucky for us, GitHub already [includes libgsl as pre-installed
software](https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-Readme.md#installed-apt-packages),
so we don't need to do anything special there.

While working on this, I noticed some tests in the LSI spec that return
early when `$GSL` is not enabled. It would be better for those tests to
report as skipped when GSL is not enabled (and this matches the pattern
of the redis tests, that report as skipped if redis isn't available).

Author: mkasberg

.github/workflows/ci.yml

@@ -14,26 +14,24 @@ on:
 
 jobs:
   ci:
-    name: "Run Tests (${{ matrix.label }})"
+    name: "Run Tests (Ruby ${{ matrix.ruby_version }}, native_vector: ${{ matrix.native_vector }})"
     runs-on: "ubuntu-latest"
     env:
       # See https://github.com/marketplace/actions/setup-ruby-jruby-and-truffleruby#matrix-of-gemfiles
       BUNDLE_GEMFILE: ${{ matrix.gemfile }}
     strategy:
       fail-fast: false
       matrix:
+        ruby_version: ["2.7", "3.0", "3.1", "jruby-9.3.4.0"]
+        native_vector: [true, false]
         include:
-          - label: Ruby 2.7
-            ruby_version: "2.7"
+          - ruby_version: "2.7"
             gemfile: Gemfile
-          - label: Ruby 3.0
-            ruby_version: "3.0"
+          - ruby_version: "3.0"
             gemfile: Gemfile
-          - label: Ruby 3.1
-            ruby_version: "3.1"
+          - ruby_version: "3.1"
             gemfile: Gemfile
-          - label: JRuby 9.3.4.0
-            ruby_version: "jruby-9.3.4.0"
+          - ruby_version: "jruby-9.3.4.0"
             gemfile: Gemfile-jruby
     steps:
       - name: Checkout Repository
@@ -43,8 +41,14 @@ jobs:
         with:
           ruby-version: ${{ matrix.ruby_version }}
           bundler-cache: true
+      - name: Install GSL Gem
+        if: ${{ !matrix.native_vector }}
+        run: gem install rb-gsl
       - name: Run Minitest based tests
         run: script/test
+        env:
+          NAVIVE_VECTOR: ${{ matrix.native_vector }}
+
     services:
       redis:
         image: redis

test/lsi/lsi_test.rb

@@ -163,7 +163,7 @@ def test_cached_content_node_option
   end
 
   def test_clears_cached_content_node_cache
-    return unless $GSL
+    skip "transposed_search_vector is only used by GSL implementation" unless $GSL
 
     lsi = ClassifierReborn::LSI.new(cache_node_vectors: true)
     lsi.add_item @str1, 'Dog'
@@ -192,7 +192,7 @@ def test_keyword_search
   end
 
   def test_invalid_searching_when_using_gsl
-    return unless $GSL
+    skip "Only GSL currently raises invalid search error" unless $GSL
 
     lsi = ClassifierReborn::LSI.new
     lsi.add_item @str1, 'Dog'