diff --git a/client/src/client/workers/test-evaluator.js b/client/src/client/workers/test-evaluator.js
index 2a8a1eaec6..c13b3c3b79 100644
--- a/client/src/client/workers/test-evaluator.js
+++ b/client/src/client/workers/test-evaluator.js
@@ -24,22 +24,37 @@ const __utils = (() => {
   }
 
   const oldLog = self.console.log.bind(self.console);
-  self.console.log = function proxyConsole(...args) {
+  function proxyLog(...args) {
     logs.push(args.map(arg => '' + JSON.stringify(arg, replacer)).join(' '));
     if (logs.join('\n').length > MAX_LOGS_SIZE) {
       flushLogs();
     }
     return oldLog(...args);
-  };
+  }
 
+  // unless data.type is truthy, this sends data out to the testRunner
   function postResult(data) {
     flushLogs();
     self.postMessage(data);
   }
 
+  function logToBoth(err) {
+    if (!(err instanceof chai.AssertionError)) {
+      // report to both the browser and the fcc consoles, discarding the
+      // stack trace via toString as it only useful to debug the site, not a
+      // specific challenge.
+      console.log(err.toString());
+    }
+  }
+
+  const toggleLogging = on => {
+    self.console.log = on ? proxyLog : () => {};
+  };
+
   return {
     postResult,
-    oldLog
+    logToBoth,
+    toggleLogging
   };
 })();
 
@@ -50,6 +65,8 @@ self.onmessage = async e => {
   const assert = chai.assert;
   // Fake Deep Equal dependency
   const DeepEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b);
+
+  __utils.toggleLogging(e.data.firstTest);
   /* eslint-enable no-unused-vars */
   try {
     let testResult;
@@ -65,14 +82,11 @@ self.onmessage = async e => {
       if (__userCodeWasExecuted) {
         // rethrow error, since test failed.
         throw err;
-      } else if (e.data.testString) {
-        // report errors to dev console if tests are running (since some
-        // challenges should pass with code that throws errors)
-        __utils.oldLog(err);
-      } else {
-        // user is editing code, so both consoles should report errors
-        console.log(err.toString());
       }
+      // log build errors
+      __utils.logToBoth(err);
+      // the tests may not require working code, so they are evaluated even if
+      // the user code does not get executed.
       testResult = eval(e.data.testString);
     }
     /* eslint-enable no-eval */
@@ -83,15 +97,17 @@ self.onmessage = async e => {
       pass: true
     });
   } catch (err) {
+    // report errors that happened during testing, so the user learns of
+    // execution errors and not just build errors.
+    __utils.toggleLogging(true);
+    __utils.logToBoth(err);
+    // postResult flushes the logs and must be called after logging is finished.
     __utils.postResult({
       err: {
         message: err.message,
         stack: err.stack
       }
     });
-    if (!(err instanceof chai.AssertionError)) {
-      console.error(err);
-    }
   }
 };
 
diff --git a/client/src/templates/Challenges/redux/execute-challenge-saga.js b/client/src/templates/Challenges/redux/execute-challenge-saga.js
index e4dbf9a771..a348776b48 100644
--- a/client/src/templates/Challenges/redux/execute-challenge-saga.js
+++ b/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 {
diff --git a/client/src/templates/Challenges/utils/build.js b/client/src/templates/Challenges/utils/build.js
index 9598e7a1dc..10300ad72a 100644
--- a/client/src/templates/Challenges/utils/build.js
+++ b/client/src/templates/Challenges/utils/build.js
@@ -99,9 +99,9 @@ function getJSTestRunner({ build, sources }, proxyLogger) {
 
   const testWorker = createWorker(testEvaluator, { terminateWorker: true });
 
-  return (testString, testTimeout) => {
+  return (testString, testTimeout, firstTest = true) => {
     return testWorker
-      .execute({ build, testString, code, sources }, testTimeout)
+      .execute({ build, testString, code, sources, firstTest }, testTimeout)
       .on('LOG', proxyLogger).done;
   };
 }