Add new ProviderGetCache class

This helper class will provide a simple cache for Resource API
provider state to minimize the number of get() calls to the
provider.

Author: seanmil

lib/puppet/resource_api/provider_get_cache.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+# rubocop:disable Style/Documentation
+module Puppet; end
+module Puppet::ResourceApi; end
+# rubocop:enable Style/Documentation
+
+# This class provides a simple caching mechanism to support minimizing get()
+# calls into a provider.
+class Puppet::ResourceApi::ProviderGetCache
+  def initialize
+    clear
+  end
+
+  def clear
+    @cache = {}
+    @cached_all = false
+  end
+
+  def all
+    raise 'all method called, but cached_all not called' unless @cached_all
+    @cache.values
+  end
+
+  def add(key, value)
+    @cache[key] = value
+  end
+
+  def get(key)
+    @cache[key]
+  end
+
+  def cached_all
+    @cached_all = true
+  end
+
+  def cached_all?
+    @cached_all
+  end
+end

spec/puppet/resource_api/provider_get_cache_spec.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Puppet::ResourceApi::ProviderGetCache do
+  subject(:cache) { described_class.new }
+
+  before(:each) do
+    cache.add(:a, 'a')
+    cache.add(:b, 'b')
+  end
+
+  describe '#add/#get' do
+    it 'sets and retrieves values from the cache' do
+      expect(cache.get(:a)).to eq 'a'
+    end
+  end
+
+  describe '#all' do
+    it 'raises an error when cached_all has not been called' do
+      expect { cache.all }.to raise_error(%r{cached_all not called})
+    end
+
+    it 'returns all values in cache when cached_all has been called' do
+      cache.cached_all
+      expect(cache.all).to eq %w[a b]
+    end
+  end
+
+  describe '#cached_all?' do
+    it 'returns false when cached_all has not been called' do
+      expect(cache.cached_all?).to be false
+    end
+
+    it 'returns true when cached_all has been called' do
+      cache.cached_all
+      expect(cache.cached_all?).to be true
+    end
+  end
+
+  describe '#clear' do
+    it 'clears the cache' do
+      cache.clear
+      expect(cache.get(:a)).to be_nil
+    end
+
+    it 'resets the cached_all flag' do
+      cache.cached_all
+      cache.clear
+      expect(cache.cached_all?).to be false
+    end
+  end
+end