diff --git a/lib/internal/v8_prof_polyfill.js b/lib/internal/v8_prof_polyfill.js
index 72efa46f041500..1bfa111d8d8ca3 100644
--- a/lib/internal/v8_prof_polyfill.js
+++ b/lib/internal/v8_prof_polyfill.js
@@ -25,6 +25,13 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+module.exports = { versionCheck };
+
+// Don't execute when required directly instead of being eval'd from
+// lib/internal/v8_prof_processor.js.  This way we can test functions
+// from this file in isolation.
+if (module.id === 'internal/v8_prof_polyfill') return;
+
 // Node polyfill
 const fs = require('fs');
 const cp = require('child_process');
@@ -64,7 +71,18 @@ const fd = fs.openSync(logFile, 'r');
 const buf = Buffer.allocUnsafe(4096);
 const dec = new (require('string_decoder').StringDecoder)('utf-8');
 var line = '';
-versionCheck();
+
+{
+  const message = versionCheck(peekline(), process.versions.v8);
+  if (message) console.log(message);
+}
+
+function peekline() {
+  const s = readline();
+  line = s + '\n' + line;
+  return s;
+}
+
 function readline() {
   while (true) {
     const lineBreak = line.indexOf('\n');
@@ -81,27 +99,21 @@ function readline() {
   }
 }
 
-function versionCheck() {
+function versionCheck(firstLine, expected) {
   // v8-version looks like
   // "v8-version,$major,$minor,$build,$patch[,$embedder],$candidate"
   // whereas process.versions.v8 is either "$major.$minor.$build-$embedder" or
   // "$major.$minor.$build.$patch-$embedder".
-  var firstLine = readline();
-  line = firstLine + '\n' + line;
   firstLine = firstLine.split(',');
-  const curVer = process.versions.v8.split(/[.\-]/);
+  const curVer = expected.split(/[.\-]/);
   if (firstLine.length !== 6 && firstLine.length !== 7 ||
       firstLine[0] !== 'v8-version') {
-    console.log('Unable to read v8-version from log file.');
-    return;
+    return 'Unable to read v8-version from log file.';
   }
   // Compare major, minor and build; ignore the patch and candidate fields.
-  for (var i = 0; i < 3; i++) {
-    if (curVer[i] !== firstLine[i + 1]) {
-      console.log('Testing v8 version different from logging version');
-      return;
-    }
-  }
+  for (var i = 0; i < 3; i++)
+    if (curVer[i] !== firstLine[i + 1])
+      return 'Testing v8 version different from logging version';
 }
 
 function macCppfiltNm(out) {