fix(coverage): fix sourcemaps of uncovered lines

packages/coverage-istanbul/src/provider.ts

@@ -211,7 +211,7 @@ export class IstanbulCoverageProvider implements CoverageProvider {
 
         const lastCoverage = this.instrumenter.lastFileCoverage()
         if (lastCoverage)
-          coverageMap.data[lastCoverage.path] = lastCoverage
+          coverageMap.addFileCoverage(lastCoverage)
       }
     }
   }

test/coverage-test/src/untested-file.ts

@@ -1,3 +1,33 @@
+/*
+ * Some top level comment which adds some padding. This helps us see
+ * if sourcemaps are off.
+*/
+
 export default function untestedFile() {
   return 'This file should end up in report when {"all": true} is given'
 }
+
+function add(a: number, b: number) {
+  // This line should NOT be covered
+  return a + b
+}
+
+function multiply(a: number, b: number) {
+  // This line should NOT be covered
+  return a * b
+}
+
+export function math(a: number, b: number, operator: '*' | '+') {
+  if (operator === '*') {
+    // This line should NOT be covered
+    return multiply(a, b)
+  }
+
+  if (operator === '+') {
+    // This line should NOT be covered
+    return add(a, b)
+  }
+
+  // This line should NOT be covered
+  throw new Error('Unsupported operator')
+}