diff --git a/javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java b/javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java
index d7f8b0a8d28..266685e0abf 100644
--- a/javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java
+++ b/javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java
@@ -434,19 +434,27 @@ public class AutoBuild {
     return true;
   }
 
+  /**
+   * Returns whether the autobuilder has seen code. 
+   * This is overridden in tests. 
+   */
+  protected boolean hasSeenCode() {
+    return seenCode;
+  }
+
   /** Perform extraction. */
   public int run() throws IOException {
     startThreadPool();
     try {
       extractSource();
       extractXml();
-      if (seenCode) { // don't bother with the externs if no code was seen
+      if (hasSeenCode()) { // don't bother with the externs if no code was seen
         extractExterns();
       }
     } finally {
       shutdownThreadPool();
     }
-    if (!seenCode) {
+    if (!hasSeenCode()) {
       if (seenFiles) {
         warn("Only found JavaScript or TypeScript files that were empty or contained syntax errors.");
       } else {
diff --git a/javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java b/javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java
index d472353067e..7c60a05d33f 100644
--- a/javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java
+++ b/javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java
@@ -119,6 +119,11 @@ public class AutoBuildTests {
           return CompletableFuture.completedFuture(null);
         }
 
+        @Override
+        protected boolean hasSeenCode() {
+          return true;
+        }
+
         @Override
         public void verifyTypeScriptInstallation(ExtractorState state) {}