fix(coverage): Do not emit error on BRDA:0 entries (#417)

Coverage report generators in Coverage.py would generate BRDA:0 for
exit branches.

Ref: https://github.com/nedbat/coveragepy/blob/5467e1f/coverage/lcovreport.py#L108-L112

Also small string fixes for error messages in BRDA.

Improves #362.

Author: cwahbong

src/test-explorer/lcov_parser.ts

@@ -360,23 +360,27 @@ export async function parseLcov(
           if (!match) {
             throw new Error(`Invalid FNDA entry`);
           }
-          const lineNumber = Number.parseInt(match[1], 10) - 1;
-          if (lineNumber < 0) {
-            throw new Error("Negative line number in DA entry");
+          const lineNumber1 = Number.parseInt(match[1], 10);
+          if (lineNumber1 < 0) {
+            throw new Error("Negative line number in BRDA entry");
           }
+          // There might be BRDA:0 for exiting branch in report generated by
+          // Coverage.py. Simply drop these entries.
+          if (lineNumber1 === 0) break;
+          const lineNumber = lineNumber1 - 1;
           const isException = match[2] === "e";
           const blockId = Number.parseInt(match[3], 10);
           const rest = match[4];
           const commaOffset = rest.lastIndexOf(",");
           if (commaOffset === undefined) {
-            throw new Error(`Invalid FNDA entry`);
+            throw new Error(`Invalid BRDA entry`);
           }
           const label = rest.substring(0, commaOffset);
           const hitCountStr = rest.substring(commaOffset + 1);
           const hitCount =
             hitCountStr === "-" ? 0 : Number.parseInt(hitCountStr, 10);
           if (hitCount < 0) {
-            throw new Error("Negative hit count in DA entry");
+            throw new Error("Negative hit count in BRDA entry");
           }
 
           if (info === undefined) {

test/lcov_parser.test.ts

@@ -71,6 +71,10 @@ describe("The lcov parser", () => {
     assert.equal(coveredFiles[0].declarationCoverage.total, 1);
   });
 
+  it("ignores invalid line numbers", async () => {
+    assert.deepEqual(await parseTestLcov("BRDA:0,0,0,b"), []);
+  });
+
   describe("parses Java coverage data:", () => {
     let fileCov: BazelFileCoverage;
     before(async () => {