fix: conditionally log non-assertion errors (JS)

console.logs and errors are only reported during the first evaluation of
the user's code.  This is because the code is evaluated for each test,
but the logs will not change between the build phases of the tests.

Errors thrown during testing (except failing assertions) are always
reported. This is to inform the user that their code is faulty, rather
than that it does not meet the challenge's requirements.

client/src/templates/Challenges/redux/execute-challenge-saga.js

@@ -92,10 +92,18 @@ function* buildChallengeData(challengeData) {
 
 function* executeTests(testRunner, tests, testTimeout = 5000) {
   const testResults = [];
-  for (const { text, testString } of tests) {
+  for (let i = 0; i < tests.length; i++) {
+    const { text, testString } = tests[i];
     const newTest = { text, testString };
+    // only the last test outputs console.logs to avoid log duplication.
+    const firstTest = i === 1;
     try {
-      const { pass, err } = yield call(testRunner, testString, testTimeout);
+      const { pass, err } = yield call(
+        testRunner,
+        testString,
+        testTimeout,
+        firstTest
+      );
       if (pass) {
         newTest.pass = true;
       } else {