Return nil as coverage instead of a File object

Given a valid pipeline job, and a regex which wouldn't match to a jobs
trace, the stream of the trace would return the File object. This was
not the case when it matched a value, as that would have been return
from the block.

Now the `extract_coverage` method returns `nil` if no match was found.

app/workers/build_coverage_worker.rb

@@ -3,7 +3,6 @@ class BuildCoverageWorker
   include BuildQueue
 
   def perform(build_id)
-    Ci::Build.find_by(id: build_id)
-      .try(:update_coverage)
+    Ci::Build.find_by(id: build_id)&.update_coverage
   end
 end

lib/gitlab/ci/trace/stream.rb

@@ -76,11 +76,14 @@ module Gitlab
           stream.each_line do |line|
             matches = line.scan(regex)
             next unless matches.is_a?(Array)
+            next if matches.empty?
 
             match = matches.flatten.last
             coverage = match.gsub(/\d+(\.\d+)?/).first
-            return coverage.to_f if coverage.present?
+            return coverage if coverage.present?
           end
+
+          nil
         rescue
           # if bad regex or something goes wrong we dont want to interrupt transition
           # so we just silentrly ignore error for now

spec/lib/gitlab/ci/trace/stream_spec.rb

@@ -167,7 +167,7 @@ describe Gitlab::Ci::Trace::Stream do
       let(:data) { 'Coverage 1033 / 1051 LOC (98.29%) covered' }
       let(:regex) { '\(\d+.\d+\%\) covered' }
 
-      it { is_expected.to eq(98.29) }
+      it { is_expected.to eq("98.29") }
     end
 
     context 'valid content & bad regex' do
@@ -188,14 +188,14 @@ describe Gitlab::Ci::Trace::Stream do
       let(:data) { ' (98.39%) covered. (98.29%) covered' }
       let(:regex) { '\(\d+.\d+\%\) covered' }
 
-      it { is_expected.to eq(98.29) }
+      it { is_expected.to eq("98.29") }
     end
 
     context 'using a regex capture' do
       let(:data) { 'TOTAL      9926   3489    65%' }
       let(:regex) { 'TOTAL\s+\d+\s+\d+\s+(\d{1,3}\%)' }
 
-      it { is_expected.to eq(65) }
+      it { is_expected.to eq("65") }
     end
   end
 end

spec/lib/gitlab/ci/trace_spec.rb

@@ -40,12 +40,24 @@ describe Gitlab::Ci::Trace do
   describe '#extract_coverage' do
     let(:regex) { '\(\d+.\d+\%\) covered' }
 
-    before do
-      trace.set('Coverage 1033 / 1051 LOC (98.29%) covered')
+    context 'matching coverage' do
+      before do
+        trace.set('Coverage 1033 / 1051 LOC (98.29%) covered')
+      end
+
+      it "returns valid coverage" do
+        expect(trace.extract_coverage(regex)).to eq("98.29")
+      end
     end
 
-    it "returns valid coverage" do
-      expect(trace.extract_coverage(regex)).to eq(98.29)
+    context 'no coverage' do
+      before do
+        trace.set('No coverage')
+      end
+
+      it 'returs nil' do
+        expect(trace.extract_coverage(regex)).to be_nil
+      end
     end
   end