fix: avoid reporting NaN coverage

fixtures/lcov.0.info

@@ -0,0 +1,3 @@
+; This is a manually generated lcov file that has no reported line founds.
+SF:/very_good_coverage/fake_lcov__no_lines_found.dart
+end_of_record

index.js

@@ -41,7 +41,7 @@ function run() {
         }
       }
     });
-    const coverage = (totalHits / totalFinds) * 100;
+    const coverage = totalFinds === 0 ? 0 : (totalHits / totalFinds) * 100;
     const isValidBuild = coverage >= minCoverage;
     const linesMissingCoverageByFile = Object.entries(linesMissingCoverage).map(
       ([file, lines]) => {

index.test.js

@@ -188,3 +188,19 @@ test('shows lines that are missing coverage when coverage is less than 100%', ()
     '/Users/felix/Development/github.com/felangel/bloc/packages/bloc/lib/src/bloc_observer.dart: 20, 27, 36, 43, 51'
   );
 });
+
+test('reports 0 coverage when no lines are found ', () => {
+  const lcovPath = './fixtures/lcov.0.info';
+  const minCoverage = 100;
+  process.env['INPUT_PATH'] = lcovPath;
+  process.env['INPUT_MIN_COVERAGE'] = minCoverage;
+  const ip = path.join(__dirname, 'index.js');
+  try {
+    cp.execSync(`node ${ip}`, { env: process.env }).toString();
+    fail('this code should fail');
+  } catch (err) {
+    expect(err).toBeDefined();
+    const errorMessage = err.stdout.toString();
+    expect(errorMessage).toContain('0 is less than min_coverage 100');
+  }
+});