[RUBY-3083] Add RSpec testing framework and initial specs

- Update CI workflow to run RSpec tests
- Add .rspec configuration file
- Update Gemfile and Gemfile.lock to include RSpec
- Generate spec_helper.rb with RSpec configuration
- Add initial Rake task spec for 'assets'

.github/workflows/ci.yml

@@ -25,3 +25,7 @@ jobs:
       - name: Run lint check
         run: |
           bundle exec rubocop --format progress --format json --out rubocop-result.json
+
+      - name: Run unit tests
+        run: |
+          bundle exec rspec

.rspec

@@ -0,0 +1 @@
+--require spec_helper

Gemfile

@@ -6,3 +6,4 @@ source "https://rubygems.org"
 gemspec
 
 gem "rake", "~> 12.0"
+gem "rspec"

Gemfile.lock

@@ -9,13 +9,27 @@ GEM
     ast (2.4.2)
     defra_ruby_style (0.2.2)
       rubocop (~> 0.82)
+    diff-lcs (1.5.1)
     parallel (1.20.1)
     parser (3.0.2.0)
       ast (~> 2.4.1)
     rainbow (3.0.0)
     rake (12.3.3)
     regexp_parser (2.1.1)
     rexml (3.2.5)
+    rspec (3.13.0)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.0)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.1)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.1)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.1)
     rubocop (0.93.1)
       parallel (~> 1.10)
       parser (>= 2.7.1.5)
@@ -38,6 +52,7 @@ DEPENDENCIES
   defra_ruby_style
   defra_ruby_template!
   rake (~> 12.0)
+  rspec
 
 BUNDLED WITH
    2.2.20

spec/spec_helper.rb

@@ -0,0 +1,98 @@
+# frozen_string_literal: true
+
+# This file was generated by the `rspec --init` command. Conventionally, all
+# specs live under a `spec` directory, which RSpec adds to the `$LOAD_PATH`.
+# The generated `.rspec` file contains `--require spec_helper` which will cause
+# this file to always be loaded, without a need to explicitly require it in any
+# files.
+#
+# Given that it is always loaded, you are encouraged to keep this file as
+# light-weight as possible. Requiring heavyweight dependencies from this file
+# will add to the boot time of your test suite on EVERY test run, even for an
+# individual file that may not need all of that loaded. Instead, consider making
+# a separate helper file that requires the additional dependencies and performs
+# the additional setup, and require it from the spec files that actually need
+# it.
+#
+# See https://rubydoc.info/gems/rspec-core/RSpec/Core/Configuration
+RSpec.configure do |config|
+  # rspec-expectations config goes here. You can use an alternate
+  # assertion/expectation library such as wrong or the stdlib/minitest
+  # assertions if you prefer.
+  config.expect_with :rspec do |expectations|
+    # This option will default to `true` in RSpec 4. It makes the `description`
+    # and `failure_message` of custom matchers include text for helper methods
+    # defined using `chain`, e.g.:
+    #     be_bigger_than(2).and_smaller_than(4).description
+    #     # => "be bigger than 2 and smaller than 4"
+    # ...rather than:
+    #     # => "be bigger than 2"
+    expectations.include_chain_clauses_in_custom_matcher_descriptions = true
+  end
+
+  # rspec-mocks config goes here. You can use an alternate test double
+  # library (such as bogus or mocha) by changing the `mock_with` option here.
+  config.mock_with :rspec do |mocks|
+    # Prevents you from mocking or stubbing a method that does not exist on
+    # a real object. This is generally recommended, and will default to
+    # `true` in RSpec 4.
+    mocks.verify_partial_doubles = true
+  end
+
+  # This option will default to `:apply_to_host_groups` in RSpec 4 (and will
+  # have no way to turn it off -- the option exists only for backwards
+  # compatibility in RSpec 3). It causes shared context metadata to be
+  # inherited by the metadata hash of host groups and examples, rather than
+  # triggering implicit auto-inclusion in groups with matching metadata.
+  config.shared_context_metadata_behavior = :apply_to_host_groups
+
+  # The settings below are suggested to provide a good initial experience
+  # with RSpec, but feel free to customize to your heart's content.
+  #   # This allows you to limit a spec run to individual examples or groups
+  #   # you care about by tagging them with `:focus` metadata. When nothing
+  #   # is tagged with `:focus`, all examples get run. RSpec also provides
+  #   # aliases for `it`, `describe`, and `context` that include `:focus`
+  #   # metadata: `fit`, `fdescribe` and `fcontext`, respectively.
+  #   config.filter_run_when_matching :focus
+  #
+  #   # Allows RSpec to persist some state between runs in order to support
+  #   # the `--only-failures` and `--next-failure` CLI options. We recommend
+  #   # you configure your source control system to ignore this file.
+  #   config.example_status_persistence_file_path = "spec/examples.txt"
+  #
+  #   # Limits the available syntax to the non-monkey patched syntax that is
+  #   # recommended. For more details, see:
+  #   # https://rspec.info/features/3-12/rspec-core/configuration/zero-monkey-patching-mode/
+  #   config.disable_monkey_patching!
+  #
+  #   # This setting enables warnings. It's recommended, but in some cases may
+  #   # be too noisy due to issues in dependencies.
+  #   config.warnings = true
+  #
+  #   # Many RSpec users commonly either run the entire suite or an individual
+  #   # file, and it's useful to allow more verbose output when running an
+  #   # individual spec file.
+  #   if config.files_to_run.one?
+  #     # Use the documentation formatter for detailed output,
+  #     # unless a formatter has already been configured
+  #     # (e.g. via a command-line flag).
+  #     config.default_formatter = "doc"
+  #   end
+  #
+  #   # Print the 10 slowest examples and example groups at the
+  #   # end of the spec run, to help surface which specs are running
+  #   # particularly slow.
+  #   config.profile_examples = 10
+  #
+  #   # Run specs in random order to surface order dependencies. If you find an
+  #   # order dependency and want to debug it, you can fix the order by providing
+  #   # the seed, which is printed after each run.
+  #   #     --seed 1234
+  #   config.order = :random
+  #
+  #   # Seed global randomization in this process using the `--seed` CLI option.
+  #   # Setting this allows you to use `--seed` to deterministically reproduce
+  #   # test failures related to randomization by passing the same `--seed` value
+  #   # as the one that triggered the failure.
+  #   Kernel.srand config.seed
+end

spec/tasks/assets_spec.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+# spec/tasks/assets_spec.rb
+
+require "rake"
+require "rspec"
+
+# Load the Rakefile
+load File.expand_path("../../Rakefile", __dir__)
+
+RSpec.describe "Rake tasks" do
+  before(:all) do
+    # Load Rake tasks
+    # Rake.application.rake_require("Rakefile")
+    Rake::Task.define_task(:environment)
+  end
+
+  describe "assets" do
+    it "runs without error" do
+      expect { Rake::Task["assets"].invoke }.not_to raise_error
+    end
+  end
+end