Print an error message if the test folder cannot be found (#11184)

Change-Id: I0642a4a51de5f989811246003415f05688f49f4e

theme-compiler/tests/src/com/vaadin/sass/testcases/scss/SassLangTests.java

@@ -32,7 +32,12 @@ public class SassLangTests extends AbstractDirectoryScanningSassTests {
     }
 
     private static URL getResourceURLInternal(String path) {
-        return SassLangTests.class.getResource("/sasslang" + path);
+        URL url = SassLangTests.class.getResource("/sasslang" + path);
+        if (url == null) {
+            throw new RuntimeException(
+                    "Could not locate /sasslang using classloader");
+        }
+        return url;
     }
 
     @TestFactory

theme-compiler/tests/src/com/vaadin/sass/testcases/scss/SassLangTestsBroken.java

@@ -32,7 +32,13 @@ public class SassLangTestsBroken extends AbstractDirectoryScanningSassTests {
     }
 
     private static URL getResourceURLInternal(String path) {
-        return SassLangTestsBroken.class.getResource("/sasslangbroken" + path);
+        URL url = SassLangTestsBroken.class.getResource("/sasslangbroken"
+                + path);
+        if (url == null) {
+            throw new RuntimeException(
+                    "Could not locate /sasslangbroken using classloader");
+        }
+        return url;
     }
 
     @TestFactory

theme-compiler/tests/src/com/vaadin/sass/testcases/scss/SassTestRunner.java

@@ -80,7 +80,7 @@ public class SassTestRunner extends BlockJUnit4ClassRunner {
                         getTestClass().getJavaClass());
             } catch (Throwable t) {
                 throw new RuntimeException("Could not run test factory method "
-                        + method.getName());
+                        + method.getName(), t);
             }
 
             // Did the factory return an array? If so, make it a list.