Add spec for webpack manifest helper

spec/lib/gitlab/webpack/manifest_spec.rb

+require 'spec_helper'
+require 'json'
+
+RSpec.describe Gitlab::Webpack::Manifest do
+  let(:manifest) do
+    <<-EOF
+      {
+        "errors": [],
+        "assetsByChunkName": {
+          "entry1": [ "entry1.js", "entry1-a.js" ],
+          "entry2": "entry2.js"
+        }
+      }
+    EOF
+  end
+
+  shared_examples_for "a valid manifest" do
+    it "should return single entry asset paths from the manifest" do
+      expect(Gitlab::Webpack::Manifest.asset_paths("entry2")).to eq(["/public_path/entry2.js"])
+    end
+
+    it "should return multiple entry asset paths from the manifest" do
+      expect(Gitlab::Webpack::Manifest.asset_paths("entry1")).to eq(["/public_path/entry1.js", "/public_path/entry1-a.js"])
+    end
+
+    it "should error on a missing entry point" do
+      expect { Gitlab::Webpack::Manifest.asset_paths("herp") }.to raise_error(Gitlab::Webpack::Manifest::AssetMissingError)
+    end
+  end
+
+  before do
+    # Test that config variables work while we're here
+    ::Rails.configuration.webpack.dev_server.host = 'hostname'
+    ::Rails.configuration.webpack.dev_server.port = 2000
+    ::Rails.configuration.webpack.manifest_filename = "my_manifest.json"
+    ::Rails.configuration.webpack.public_path = "public_path"
+    ::Rails.configuration.webpack.output_dir = "manifest_output"
+  end
+
+  context "with dev server enabled" do
+    before do
+      ::Rails.configuration.webpack.dev_server.enabled = true
+
+      stub_request(:get, "http://hostname:2000/public_path/my_manifest.json").to_return(body: manifest, status: 200)
+    end
+
+    describe :asset_paths do
+      it_should_behave_like "a valid manifest"
+
+      it "should error if we can't find the manifest" do
+        ::Rails.configuration.webpack.manifest_filename = "broken.json"
+        stub_request(:get, "http://hostname:2000/public_path/broken.json").to_raise(SocketError)
+
+        expect { Gitlab::Webpack::Manifest.asset_paths("entry1") }.to raise_error(Gitlab::Webpack::Manifest::ManifestLoadError)
+      end
+
+      describe "webpack errors" do
+        context "when webpack has 'Module build failed' errors in its manifest" do
+          it "should error" do
+            error_manifest = JSON.parse(manifest).merge("errors" => [
+              "somethingModule build failed something",
+              "I am an error"
+            ]).to_json
+            stub_request(:get, "http://hostname:2000/public_path/my_manifest.json").to_return(body: error_manifest, status: 200)
+
+            expect { Gitlab::Webpack::Manifest.asset_paths("entry1") }.to raise_error(Gitlab::Webpack::Manifest::WebpackError)
+          end
+        end
+
+        context "when webpack does not have 'Module build failed' errors in its manifest" do
+          it "should not error" do
+            error_manifest = JSON.parse(manifest).merge("errors" => ["something went wrong"]).to_json
+            stub_request(:get, "http://hostname:2000/public_path/my_manifest.json").to_return(body: error_manifest, status: 200)
+
+            expect { Gitlab::Webpack::Manifest.asset_paths("entry1") }.to_not raise_error
+          end
+        end
+
+        it "should not error if errors is present but empty" do
+          error_manifest = JSON.parse(manifest).merge("errors" => []).to_json
+          stub_request(:get, "http://hostname:2000/public_path/my_manifest.json").to_return(body: error_manifest, status: 200)
+          expect { Gitlab::Webpack::Manifest.asset_paths("entry1") }.to_not raise_error
+        end
+      end
+    end
+  end
+
+  context "with dev server disabled" do
+    before do
+      ::Rails.configuration.webpack.dev_server.enabled = false
+      allow(File).to receive(:read).with(::Rails.root.join("manifest_output/my_manifest.json")).and_return(manifest)
+    end
+
+    describe :asset_paths do
+      it_should_behave_like "a valid manifest"
+
+      it "should error if we can't find the manifest" do
+        ::Rails.configuration.webpack.manifest_filename = "broken.json"
+        allow(File).to receive(:read).with(::Rails.root.join("manifest_output/broken.json")).and_raise(Errno::ENOENT)
+        expect { Gitlab::Webpack::Manifest.asset_paths("entry1") }.to raise_error(Gitlab::Webpack::Manifest::ManifestLoadError)
+      end
+    end
+  end
+end
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