add extension test, change restrictions default from false to null — makes more sense

src/core/Core.js

@@ -43,10 +43,10 @@ class Uppy {
       autoProceed: true,
       debug: false,
       restrictions: {
-        maxFileSize: false,
-        maxNumberOfFiles: false,
-        minNumberOfFiles: false,
-        allowedFileTypes: false
+        maxFileSize: null,
+        maxNumberOfFiles: null,
+        minNumberOfFiles: null,
+        allowedFileTypes: null
       },
       meta: {},
       onBeforeFileAdded: (currentFile, files) => currentFile,

src/core/Core.test.js

@@ -1020,7 +1020,7 @@ describe('src/Core', () => {
 
     xit('should enforce the minNumberOfFiles rule', () => {})
 
-    it('should enfore the allowedFileTypes rule', () => {
+    it('should enforce the allowedFileTypes rule', () => {
       const core = new Core({
         autoProceed: false,
         restrictions: {
@@ -1042,6 +1042,28 @@ describe('src/Core', () => {
       }
     })
 
+    it('should enforce the allowedFileTypes rule with file extensions', () => {
+      const core = new Core({
+        autoProceed: false,
+        restrictions: {
+          allowedFileTypes: ['.gif', '.jpg', '.jpeg']
+        }
+      })
+
+      try {
+        core.addFile({
+          source: 'jest',
+          name: 'foo2.png',
+          type: '',
+          data: new File([sampleImage], { type: 'image/jpeg' })
+        })
+        throw new Error('should have thrown')
+      } catch (err) {
+        expect(err).toMatchObject(new Error('You can only upload: .gif, .jpg, .jpeg'))
+        expect(core.state.info.message).toEqual('You can only upload: .gif, .jpg, .jpeg')
+      }
+    })
+
     it('should enforce the maxFileSize rule', () => {
       const core = new Core({
         autoProceed: false,
@@ -1273,7 +1295,7 @@ describe('src/Core', () => {
       })
 
       expect(core.opts.restrictions.maxNumberOfFiles).toBe(3)
-      expect(core.opts.restrictions.minNumberOfFiles).toBe(false)
+      expect(core.opts.restrictions.minNumberOfFiles).toBe(null)
     })
   })
 })