Add parser for helm list

Will be required in later MRs to parse the cluster_application artifact

lib/gitlab/kubernetes/helm/parsers/list_v2.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Kubernetes
+    module Helm
+      module Parsers
+        # Parses Helm v2 list (JSON) output
+        class ListV2
+          ParserError = Class.new(StandardError)
+
+          attr_reader :contents, :json
+
+          def initialize(contents)
+            @contents = contents
+            @json = Gitlab::Json.parse(contents)
+          rescue JSON::ParserError => e
+            raise ParserError, e.message
+          end
+
+          def releases
+            @releases ||= json["Releases"] || []
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/kubernetes/helm/parsers/list_v2_spec.rb

+# frozen_string_literal: true
+
+require 'fast_spec_helper'
+
+describe Gitlab::Kubernetes::Helm::Parsers::ListV2 do
+  let(:valid_file_contents) do
+    <<~EOF
+    {
+      "Next": "",
+      "Releases": [
+        {
+          "Name": "certmanager",
+          "Revision": 2,
+          "Updated": "Sun Mar 29 06:55:42 2020",
+          "Status": "DEPLOYED",
+          "Chart": "cert-manager-v0.10.1",
+          "AppVersion": "v0.10.1",
+          "Namespace": "gitlab-managed-apps"
+        },
+        {
+          "Name": "certmanager-crds",
+          "Revision": 2,
+          "Updated": "Sun Mar 29 06:55:32 2020",
+          "Status": "DEPLOYED",
+          "Chart": "cert-manager-crds-v0.2.0",
+          "AppVersion": "release-0.10",
+          "Namespace": "gitlab-managed-apps"
+        },
+        {
+          "Name": "certmanager-issuer",
+          "Revision": 1,
+          "Updated": "Tue Feb 18 10:04:04 2020",
+          "Status": "FAILED",
+          "Chart": "cert-manager-issuer-v0.1.0",
+          "AppVersion": "",
+          "Namespace": "gitlab-managed-apps"
+        },
+        {
+          "Name": "runner",
+          "Revision": 2,
+          "Updated": "Sun Mar 29 07:01:01 2020",
+          "Status": "DEPLOYED",
+          "Chart": "gitlab-runner-0.14.0",
+          "AppVersion": "12.8.0",
+          "Namespace": "gitlab-managed-apps"
+        }
+      ]
+    }
+    EOF
+  end
+
+  describe '#initialize' do
+    it 'initializes without error' do
+      expect do
+        described_class.new(valid_file_contents)
+      end.not_to raise_error
+    end
+
+    it 'raises an error on invalid JSON' do
+      expect do
+        described_class.new('')
+      end.to raise_error(described_class::ParserError, 'A JSON text must at least contain two octets!')
+    end
+  end
+
+  describe '#releases' do
+    subject(:list_v2) { described_class.new(valid_file_contents) }
+
+    it 'returns list of releases' do
+      expect(list_v2.releases).to match([
+        a_hash_including('Name' => 'certmanager', 'Status' => 'DEPLOYED'),
+        a_hash_including('Name' => 'certmanager-crds', 'Status' => 'DEPLOYED'),
+        a_hash_including('Name' => 'certmanager-issuer', 'Status' => 'FAILED'),
+        a_hash_including('Name' => 'runner', 'Status' => 'DEPLOYED')
+      ])
+    end
+
+    context 'empty Releases' do
+      let(:valid_file_contents) { '{}' }
+
+      it 'returns an empty array' do
+        expect(list_v2.releases).to eq([])
+      end
+    end
+  end
+end