Create method that checks if build has been erased

+ minor improvements

app/models/ci/build/eraseable.rb

@@ -26,16 +26,18 @@ module Ci
         end
       end
 
+      def erased?
+        !self.erased_at.nil?
+      end
+
       private
 
       def erase_trace!
-        File.truncate(path_to_trace, 0) if File.file?(path_to_trace)
+        self.trace = nil
       end
 
       def update_erased!(user = nil)
-        self.erased_by = user if user
-        self.erased_at = Time.now
-        self.save!
+        self.update(erased_by: user, erased_at: Time.now)
       end
     end
   end

features/steps/project/builds/summary.rb

@@ -18,7 +18,7 @@ class Spinach::Features::ProjectBuildsSummary < Spinach::FeatureSteps
   step 'recent build has been erased' do
     expect(@build.artifacts_file.exists?).to be_falsy
     expect(@build.artifacts_metadata.exists?).to be_falsy
-    expect(File.zero?(@build.path_to_trace)).to be true
+    expect(@build.trace).to be_empty
   end
 
   step 'recent build summary does not have artifacts widget' do

spec/models/ci/build/eraseable_spec.rb

@@ -11,7 +11,7 @@ describe Ci::Build::Eraseable, models: true do
     end
 
     it 'should erase build trace in trace file' do
-      expect(File.zero?(build.path_to_trace)).to eq true
+      expect(build.trace).to be_empty
     end
 
     it 'should set erased to true' do
@@ -78,6 +78,21 @@ describe Ci::Build::Eraseable, models: true do
       it { is_expected.to be_truthy }
     end
 
+    describe '#erased?' do
+      let!(:build) { create(:ci_build_with_trace, :success, :artifacts) }
+      subject { build.erased? }
+
+      context 'build has not been erased' do
+        it { is_expected.to be false }
+      end
+
+      context 'build has been erased' do
+        before { build.erase! }
+
+        it { is_expected.to be true }
+      end
+    end
+
     context 'metadata and build trace are not available' do
       let!(:build) { create(:ci_build, :success, :artifacts) }
       before { build.remove_artifacts_metadata! }