Git Commit Sha - fix loose matching error and add comments

Author: robwise

Diff for: app/helpers/pages_helper.rb

@@ -5,6 +5,6 @@ def git_commit_sha
 
   def git_commit_sha_short
     full_sha = git_commit_sha
-    full_sha[-8..-1]
+    full_sha[-7..-1]
   end
 end

Diff for: app/models/git_commit_sha.rb

@@ -1,23 +1,25 @@
 # Retrieves the current git commit SHA of the project
 class GitCommitSha
   def self.current_sha
-    @commit_sha ||= retrieve_sha_from_file.presence || retrieve_sha_from_git
+    @sha ||= retrieve_sha_from_file.presence || retrieve_sha_from_git
   end
 
   def self.current_sha=(sha)
-    @commit_sha = sha
+    @sha = sha
   end
 
   def self.reset_current_sha
     self.current_sha = nil
   end
 
+  # Assumes the git CLI is available. This is not the case in production on Heroku.
   def self.retrieve_sha_from_git
     `git rev-parse HEAD 2>/dev/null`.to_s.strip
   end
 
+  # Assumes a .source_version file with SHA inside. A special Heroku buildpack creates this for us in production.
   def self.retrieve_sha_from_file
     expected_filepath = Rails.root.join(".source_version")
-    File.exist?(expected_filepath) ? File.read(expected_filepath) : nil
+    File.exist?(expected_filepath) ? File.read(expected_filepath).to_s.strip : nil
   end
 end

Diff for: spec/features/pages_spec.rb

@@ -1,29 +1,33 @@
 require "rails_helper"
 
 shared_examples "Git Commit SHA" do
-  # Keep existing env variable intact
-  let!(:old_sha) { ENV["DEPLOYMENT_SHA"] }
-  after { ENV["DEPLOYMENT_SHA"] = old_sha }
   background { visit root_path }
   it "displays the current git commit" do
-    expect(page).to have_css("#git-commit-sha", text: expected_text)
+    el = find("#git-commit-sha")
+    expect(el.text).to eq expected_text
   end
 end
 
 feature "Git Commit SHA" do
+  before do
+    # sha gets cached as an instance variable, so need to start fresh
+    GitCommitSha.reset_current_sha
+  end
+
   context "when .source_version file does not exist" do
     let(:sha) { "94d92356828a56db25fccff9d50f41c525eead5x" }
     let(:expected_text) { "5eead5x" }
-    before { GitCommitSha.current_sha = sha }
+    before do
+      # stub this method since we need to control what the sha actually is
+      allow(GitCommitSha).to receive(:retrieve_sha_from_git) { sha }
+    end
     it_behaves_like "Git Commit SHA"
   end
+
   context "when .source_version file exists" do
     let(:sha) { "94d92356828a56db25fccff9d50f41c525eead5y" }
     let(:expected_text) { "5eead5y" }
-    before do
-      `cd #{Rails.root} && echo #{sha} > .source_version`
-      GitCommitSha.reset_current_sha
-    end
+    before { `cd #{Rails.root} && echo #{sha} > .source_version` }
     after { `cd #{Rails.root} && rm .source_version` }
     it_behaves_like "Git Commit SHA"
   end