Refactor improve implementations validation

src/options.json

@@ -2,7 +2,8 @@
   "type": "object",
   "properties": {
     "implementation": {
-      "description": "The implementation of the sass to be used (https://github.com/webpack-contrib/sass-loader#implementation)."
+      "description": "The implementation of the sass to be used (https://github.com/webpack-contrib/sass-loader#implementation).",
+      "type": "object"
     },
     "sassOptions": {
       "description": "Options for `node-sass` or `sass` (`Dart Sass`) implementation. (https://github.com/webpack-contrib/sass-loader#implementation).",

test/__snapshots__/validate-options.test.js.snap

@@ -1,6 +1,13 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`validate options 1`] = `
+"Invalid options object. Sass Loader has been initialised using an options object that does not match the API schema.
+ - options.implementation should be an object:
+   object { … }
+   -> The implementation of the sass to be used (https://github.com/webpack-contrib/sass-loader#implementation)."
+`;
+
+exports[`validate options 2`] = `
 "Invalid options object. Sass Loader has been initialised using an options object that does not match the API schema.
  - options.sassOptions should be one of these:
    object { … } | function
@@ -11,7 +18,7 @@ exports[`validate options 1`] = `
     * options.sassOptions should be an instance of function."
 `;
 
-exports[`validate options 2`] = `
+exports[`validate options 3`] = `
 "Invalid options object. Sass Loader has been initialised using an options object that does not match the API schema.
  - options.prependData should be one of these:
    string | function
@@ -21,13 +28,13 @@ exports[`validate options 2`] = `
     * options.prependData should be an instance of function."
 `;
 
-exports[`validate options 3`] = `
+exports[`validate options 4`] = `
 "Invalid options object. Sass Loader has been initialised using an options object that does not match the API schema.
  - options.webpackImporter should be a boolean.
    -> Enables/Disables default \`webpack\` importer (https://github.com/webpack-contrib/sass-loader#webpackimporter)."
 `;
 
-exports[`validate options 4`] = `
+exports[`validate options 5`] = `
 "Invalid options object. Sass Loader has been initialised using an options object that does not match the API schema.
  - options has an unknown property 'unknown'. These properties are valid:
    object { implementation?, sassOptions?, prependData?, sourceMap?, webpackImporter? }"

test/validate-options.test.js

@@ -20,11 +20,17 @@ it('validate options', () => {
       'a { color: red; }'
     );
 
-  // eslint-disable-next-line global-require
-  // expect(() => validate({ implementation: require('node-sass') })).not.toThrow();
-  // eslint-disable-next-line global-require
-  // expect(() => validate({ implementation: require('sass') })).not.toThrow();
-  // expect(() => validate({ implementation: true })).not.toThrow();
+  expect(() =>
+    // eslint-disable-next-line global-require
+    validate({ implementation: require('node-sass') })
+  ).not.toThrow();
+  expect(() =>
+    // eslint-disable-next-line global-require
+    validate({ implementation: require('sass') })
+  ).not.toThrow();
+  expect(() =>
+    validate({ implementation: true })
+  ).toThrowErrorMatchingSnapshot();
 
   expect(() => validate({ sassOptions: {} })).not.toThrow();
   expect(() =>