add test for initial error matcher

src/error_matcher.test.ts

@@ -0,0 +1,33 @@
+
+import test from 'ava';
+
+import { namedMatchersForTesting } from './error_matcher';
+
+/*
+NB We test the regexes for all the matchers against example log output snippets.
+*/
+
+test('noSourceCodeFound matches against example javascript output', async t => {
+  t.assert(testErrorMatcher("noSourceCodeFound", `
+  2020-09-07T17:39:53.9050522Z [2020-09-07 17:39:53] [build] Done extracting /opt/hostedtoolcache/CodeQL/0.0.0-20200630/x64/codeql/javascript/tools/data/externs/web/ie_vml.js (3 ms)
+  2020-09-07T17:39:53.9051849Z [2020-09-07 17:39:53] [build-err] No JavaScript or TypeScript code found.
+  2020-09-07T17:39:53.9052444Z [2020-09-07 17:39:53] [build-err] No JavaScript or TypeScript code found.
+  2020-09-07T17:39:53.9251124Z [2020-09-07 17:39:53] [ERROR] Spawned process exited abnormally (code 255; tried to run: [/opt/hostedtoolcache/CodeQL/0.0.0-20200630/x64/codeql/javascript/tools/autobuild.sh])
+  `));
+});
+
+function testErrorMatcher(matcherName: string, logSample: string): boolean {
+
+  const regex = namedMatchersForTesting[matcherName] ? namedMatchersForTesting[matcherName][1] : null;
+
+  if (regex) {
+    return regex.test(logSample);
+  } else {
+    if (namedMatchersForTesting[matcherName]) {
+      throw new Error(`Cannot test matcher ${matcherName} with null regex`);
+    } else {
+      throw new Error(`Unknown matcher ${matcherName}`);
+    }
+  }
+
+}

src/error_matcher.ts

@@ -1,19 +1,19 @@
 
 export type ErrorMatcher = [number|null, RegExp|null, string];
 
-const namedMatchers: { [key: string]: ErrorMatcher } = {
+// exported only for testing purposes
+export const namedMatchersForTesting: { [key: string]: ErrorMatcher } = {
+  /*
+  In due course it may be possible to remove the regex, if/when javascript also exits with code 32.
+   For context see https://github.com/github/semmle-code/pull/36921
+  */
   noSourceCodeFound: [
     32,
-    null,
-    `No source code was seen during the build. Please see...
-https://docs.github.com/en/github/finding-security-vulnerabilities-and-errors-in-your-code/troubleshooting-code-scanning#no-code-found-during-the-build`
-  ],
-  noSourceCodeFoundJavascript: [
-    null,
     new RegExp("No JavaScript or TypeScript code found\\."),
     `No source code was seen during the build. Please see...
 https://docs.github.com/en/github/finding-security-vulnerabilities-and-errors-in-your-code/troubleshooting-code-scanning#no-code-found-during-the-build`
-  ]
+  ],
 };
 
-export const errorMatchers = Object.values(namedMatchers);
+// we collapse the matches into an array for use in exec_wrapper
+export const errorMatchers = Object.values(namedMatchersForTesting);