Update #uncommitted_changes? to handle missing Git

- Fix for GitUtils.uncommitted_changes? throwing an error when called in
  an environment that does not have git installed
- Add tests for GitUtils.uncommitted_changes? scenariors
- Fixes shakacode#888

CHANGELOG.md

@@ -8,6 +8,8 @@ Changes since last non-beta release.
 
 *Please add entries here for your pull requests.*
 
+- Fixes GitUtils.uncommitted_changes? throwing an error when called in an environment without Git, and allows install generator to be run successfully with `--ignore-warnings` [#878](https://github.com/shakacode/react_on_rails/pull/878) by [jasonblalock](https://github.com/jasonblalock)
+
 ## [8.0.4]
 ### Fixed
  - Corrects `devBuild` value for webpack production build from webpackConfigLoader. [#877](https://github.com/shakacode/react_on_rails/pull/877) by [chenqingspring](https://github.com/chenqingspring).
@@ -19,9 +21,9 @@ Changes since last non-beta release.
 
 ## [8.0.2]
 ### Fixed
-- Any failure in webpack to build test files quits tests. 
+- Any failure in webpack to build test files quits tests.
 - Fixed a Ruby 2.4 potential crash which could cause a crash due to pathname change in Ruby 2.4.
-- CI Improvements: 
+- CI Improvements:
   - Switched to yarn link and removed relative path install of react-on-rails
   - Removed testing of Turbolinks 2
   - All tests run against Rails 5.1.1
@@ -45,7 +47,7 @@ Changes since last non-beta release.
 ### Changed
 - Major updates for WebpackerLite 2.0.2. [#844](https://github.com/shakacode/react_on_rails/pull/845) by [justin808](https://github.com/justin808) with help from ](https://github.com/robwise)
 - Logging no longer occurs when trace is turned to false. [#845](https://github.com/shakacode/react_on_rails/pull/845) by [conturbo](https://github.com/Conturbo)
-                               
+
 ## [8.0.0-beta.2] - 2017-05-08
 
 ### Changed

lib/react_on_rails/git_utils.rb

@@ -5,7 +5,7 @@ module GitUtils
     def self.uncommitted_changes?(message_handler)
       return false if ENV["COVERAGE"] == "true"
       status = `git status --porcelain`
-      return false if status.empty?
+      return false if !status.nil? && status.empty?
       error = "You have uncommitted code. Please commit or stash your changes before continuing"
       message_handler.add_error(error)
       true

spec/react_on_rails/git_utils_spec.rb

@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require_relative "spec_helper"
+
+module ReactOnRails
+  RSpec.describe GitUtils do
+    describe ".uncommitted_changes?" do
+      context "With uncommited git changes" do
+        subject { "M file/path" }
+        let(:message_handler) { instance_double("MessageHandler") }
+
+        before do
+          allow(described_class).to receive(:`).with("git status --porcelain").and_return(subject)
+          expect(message_handler).to receive(:add_error)
+            .with("You have uncommitted code. Please commit or stash your changes before continuing")
+        end
+
+        it "returns true" do
+          expect(described_class.uncommitted_changes?(message_handler)).to eq(true)
+        end
+      end
+
+      context "With clean git status" do
+        subject { "" }
+        let(:message_handler) { instance_double("MessageHandler") }
+
+        before do
+          allow(described_class).to receive(:`).with("git status --porcelain").and_return(subject)
+          expect(message_handler).not_to receive(:add_error)
+        end
+
+        it "returns false" do
+          expect(described_class.uncommitted_changes?(message_handler)).to eq(false)
+        end
+      end
+
+      context "With git status failure" do
+        subject { nil }
+        let(:message_handler) { instance_double("MessageHandler") }
+
+        before do
+          allow(described_class).to receive(:`).with("git status --porcelain").and_return(subject)
+          expect(message_handler).to receive(:add_error)
+            .with("You have uncommitted code. Please commit or stash your changes before continuing")
+        end
+
+        it "returns true" do
+          expect(described_class.uncommitted_changes?(message_handler)).to eq(true)
+        end
+      end
+    end
+  end
+end