JS: Fix virtual source root in AutoBuildTest

Author: asgerf

javascript/extractor/src/com/semmle/js/extractor/AutoBuild.java

@@ -231,13 +231,17 @@ public AutoBuild() {
         Env.systemEnv()
             .getInt(
                 "LGTM_INDEX_TYPESCRIPT_INSTALL_DEPS_TIMEOUT", INSTALL_DEPENDENCIES_DEFAULT_TIMEOUT);
-    this.virtualSourceRoot = new VirtualSourceRoot(LGTM_SRC, toRealPath(Paths.get(EnvironmentVariables.getScratchDir())));
+    this.virtualSourceRoot = makeVirtualSourceRoot();
     setupFileTypes();
     setupXmlMode();
     setupMatchers();
     this.state = new ExtractorState();
   }
 
+  protected VirtualSourceRoot makeVirtualSourceRoot() {
+    return new VirtualSourceRoot(LGTM_SRC, toRealPath(Paths.get(EnvironmentVariables.getScratchDir())));
+  }
+
   private String getEnvVar(String envVarName) {
     return getEnvVar(envVarName, null);
   }

javascript/extractor/src/com/semmle/js/extractor/test/AutoBuildTests.java

@@ -28,6 +28,7 @@
 import com.semmle.js.extractor.ExtractorState;
 import com.semmle.js.extractor.FileExtractor;
 import com.semmle.js.extractor.FileExtractor.FileType;
+import com.semmle.js.extractor.VirtualSourceRoot;
 import com.semmle.util.data.StringUtil;
 import com.semmle.util.exception.UserError;
 import com.semmle.util.files.FileUtil;
@@ -137,6 +138,11 @@ protected DependencyInstallationResult preparePackagesAndDependencies(Set<Path>
           return DependencyInstallationResult.empty;
         }
 
+        @Override
+        protected VirtualSourceRoot makeVirtualSourceRoot() {
+          return VirtualSourceRoot.none; // not used in these tests
+        }
+
         @Override
         protected void extractXml() throws IOException {
           Files.walkFileTree(