fix: Check if commands include at least one of "url", "file" or "wait" parameters

Fail, if the command object is empty.

Author: prantlf

Gruntfile.js

@@ -130,6 +130,31 @@ module.exports = function (grunt) {
             file: 'dynamic-third.html'
           }
         ]
+      },
+      'no-input': {
+        options: {
+          force: true
+        },
+        pages: [
+          {}
+        ]
+      },
+      'invalid-file': {
+        options: {
+          force: true
+        },
+        '//': {
+          url: 'http://localhost:8881'
+        }
+      },
+      'invalid-dest': {
+        options: {
+          dest: '//',
+          force: true
+        },
+        dummy: {
+          url: 'http://localhost:8881'
+        }
       }
     },
 

tasks/html-dom-snapshot.js

@@ -84,6 +84,10 @@ module.exports = function (grunt) {
       if (url) {
         grunt.verbose.writeln('Taking a snapshot of ' + url + '...');
       } else {
+        if (!(file || wait)) {
+          throw new Error('Missing parameters "url", "file" or "wait" ' +
+              'in the target "' + target + '".');
+        }
         grunt.verbose.writeln('Preparing the next snapshot...');
       }
       return client.setViewportSize(pageOptions.viewport)