diff --git a/lib/mailer.js b/lib/mailer.js
index 07e3802..ec6d8ec 100644
--- a/lib/mailer.js
+++ b/lib/mailer.js
@@ -187,7 +187,7 @@ const factory = (options) => {
       // `preview` prop in the data context to apply to the layout.
       if (tmpl.__helpers.has('preview')) {
         preview = tmpl.__helpers.get('preview');
-      } else if (data.preview) {
+      } else if (data && data.preview) {  // data is optional
         preview = data.preview;
       }
 
diff --git a/lib/utils.js b/lib/utils.js
index 71fdd8f..b0bf80d 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -22,6 +22,21 @@ const sass = (function() {
   return null;
 })();
 
+/**
+ * Check if file exists
+ * @param  {String} filePath
+ * @return {Boolean}
+ */
+const fileExists = function (filePath) {
+  try {
+    return fs.statSync(filePath).isFile();
+  }
+  catch (err)
+  {
+      return false;
+  }
+}
+
 const TAG = 'mailer-utils';
 
 // This package assumes that assets (templates, SCSS, CSS ..) are
@@ -37,7 +52,6 @@ const TAG = 'mailer-utils';
 //     /var/www/app/bundle
 //
 // For Modulus, you need to use the `APP_DIR` variable, which you do NOT need to set.
-
 const developmentPrivateDir = () => {
   if (!isDevEnv) {
     return '';
@@ -154,7 +168,21 @@ Utils = {
   },
 
   readFile(relativePathFromApp) {
-    const file = Path.join(ROOT, relativePathFromApp);
+    let file
+    if (Meteor.isAppTest
+      || Meteor.isTest) {
+      // note:
+      //  * this DOES WORK with Meteor.isTest (=unit test mode)
+      //  * Meteor.isAppTest is NOT TESTED yet (=in-app test mode)
+      //
+      // background-info: we had NO luck with "Assets.absoluteFilePath(relativePathFromApp)",
+      //  so lets build the path ourselves.
+      //  see discussion https://github.com/lookback/meteor-emails/issues/76
+      file = Path.join(process.cwd(), 'assets', 'app', relativePathFromApp);
+    } else {
+      // = standard mode (development || production)
+      file = Path.join(ROOT, relativePathFromApp);
+    }
 
     try {
       return fs.readFileSync(file, {
@@ -178,17 +206,29 @@ ${packageToRecommend}`, TAG);
       return Utils.readFile(scss);
     }
 
-    const file = Path.join(ROOT, scss);
+    let file
+    if (Meteor.isAppTest
+      || Meteor.isTest) {
+      // note:
+      //  * this DOES WORK with Meteor.isTest (=unit test mode)
+      //  * Meteor.isAppTest is NOT TESTED yet (=in-app test mode)
+      file = Path.join(process.cwd(), 'assets', 'app', scss);
+    } else {
+      // = standard mode (development || production)
+      file = Path.join(ROOT, scss);
+    }
 
-    try {
-      return sass.renderSync({
-        file: file,
-        sourceMap: false
-      }).css.toString();
-    } catch (ex) {
-      console.error(`Sass failed to compile: ${ex.message}`);
-      console.error(`In ${ex.file || scss} at line ${ex.line}, column ${ex.column}`);
-      return '';
+    if (fileExists(file)) {
+      try {
+        return sass.renderSync({
+          file: file,
+          sourceMap: false
+        }).css.toString();
+      } catch (ex) {
+        console.error(`Sass failed to compile: ${ex.message}`);
+        console.error(`In ${ex.file || scss} at line ${ex.line}, column ${ex.column}`);
+      }
     }
+    return '';  // fallback: on error, or if file does NOT exist
   }
 };