fix(import-preview): COMPASS-4212: handle edge cases where we can't show

src/components/import-preview/import-preview.jsx

@@ -127,9 +127,18 @@ class ImportPreview extends PureComponent {
   };
 
   render() {
-    if (!this.props.loaded) {
+    const { loaded, fields, values } = this.props;
+
+    if (!loaded) {
+      debug('Preview unavailable: not loaded yet');
       return null;
     }
+
+    if (!Array.isArray(fields) || !Array.isArray(values)) {
+      debug('Preview unavailable: Fields or values is not an array', { fields, values });
+      return null;
+    }
+
     return (
       <div className={style()}>
         <div className={style('header')}>Specify Fields and Types</div>

src/components/import-preview/import-preview.spec.js

@@ -0,0 +1,100 @@
+import React from 'react';
+import { mount } from 'enzyme';
+
+import ImportPreview from './';
+import createStyler from 'utils/styler.js';
+import styles from './import-preview.less';
+
+let onFieldCheckedChangedSpy;
+let setFieldTypeSpy;
+
+describe('ImportPreview [Component]', () => {
+  describe('not loaded', () => {
+    let component;
+
+    before(() => {
+      onFieldCheckedChangedSpy = sinon.spy();
+      setFieldTypeSpy = sinon.spy();
+
+      component = mount(
+        <ImportPreview
+          fields={[['_id']]}
+          values={[[1]]}
+          loaded={false}
+          onFieldCheckedChanged={onFieldCheckedChangedSpy}
+          setFieldType={setFieldTypeSpy}
+        />
+      );
+    });
+
+    it('should not render', () => {
+      const style = createStyler(styles, 'import-preview');
+      expect(component.find(`.${style()}`)).to.not.be.present();
+    });
+
+    after(() => {
+      component = null;
+      onFieldCheckedChangedSpy = null;
+      setFieldTypeSpy = null;
+    });
+  });
+  describe('no fields', () => {
+    let component;
+
+    before(() => {
+      onFieldCheckedChangedSpy = sinon.spy();
+      setFieldTypeSpy = sinon.spy();
+
+      component = mount(
+        <ImportPreview
+          fields={null}
+          values={[[1, 2]]}
+          loaded
+          onFieldCheckedChanged={onFieldCheckedChangedSpy}
+          setFieldType={setFieldTypeSpy}
+        />
+      );
+    });
+
+    it('should not render', () => {
+      const style = createStyler(styles, 'import-preview');
+      expect(component.find(`.${style()}`)).to.not.be.present();
+    });
+
+    after(() => {
+      component = null;
+      onFieldCheckedChangedSpy = null;
+      setFieldTypeSpy = null;
+    });
+  });
+
+  describe('no fields', () => {
+    let component;
+
+    before(() => {
+      onFieldCheckedChangedSpy = sinon.spy();
+      setFieldTypeSpy = sinon.spy();
+
+      component = mount(
+        <ImportPreview
+          fields={[['_id']]}
+          values={null}
+          loaded
+          onFieldCheckedChanged={onFieldCheckedChangedSpy}
+          setFieldType={setFieldTypeSpy}
+        />
+      );
+    });
+
+    it('should not render', () => {
+      const style = createStyler(styles, 'import-preview');
+      expect(component.find(`.${style()}`)).to.not.be.present();
+    });
+
+    after(() => {
+      component = null;
+      onFieldCheckedChangedSpy = null;
+      setFieldTypeSpy = null;
+    });
+  });
+});

src/modules/import.js

@@ -367,7 +367,7 @@ const loadPreviewDocs = (
      * actually need it.
      */
     const source = fs.createReadStream(fileName, {encoding: 'utf8', end: 20 * 1024});
-    const dest = createPreviewWritable();
+    const dest = createPreviewWritable(fileType, delimiter, fileIsMultilineJSON);
     stream.pipeline(
       source,
       createPeekStream(fileType, delimiter, fileIsMultilineJSON),