Updates file unit tests to be Windows compatible (elastic#24281)

Signed-off-by: Tyler Smalley <tyler.smalley@elastic.co>

src/dev/__tests__/file.js

@@ -17,7 +17,7 @@
  * under the License.
  */
 
-import { resolve } from 'path';
+import { resolve, sep } from 'path';
 
 import expect from 'expect.js';
 
@@ -38,7 +38,7 @@ describe('dev/File', () => {
   describe('#getRelativePath()', () => {
     it('returns the path relative to the repo root', () => {
       const file = new File(HERE);
-      expect(file.getRelativePath()).to.eql('src/dev/__tests__/file.js');
+      expect(file.getRelativePath()).to.eql(['src', 'dev', '__tests__', 'file.js'].join(sep));
     });
   });
 
@@ -69,8 +69,8 @@ describe('dev/File', () => {
     it('returns the parents of a file, stopping at the repo root, in descending order', () => {
       const file = new File(HERE);
       expect(file.getRelativeParentDirs()).to.eql([
-        'src/dev/__tests__',
-        'src/dev',
+        ['src', 'dev', '__tests__'].join(sep), // src/dev/__tests__
+        ['src', 'dev'].join(sep), // src/dev
         'src',
       ]);
     });

src/dev/npm/__tests__/installed_packages.js

@@ -17,7 +17,7 @@
  * under the License.
  */
 
-import { resolve } from 'path';
+import { resolve, sep } from 'path';
 
 import { uniq } from 'lodash';
 import expect from 'expect.js';
@@ -61,15 +61,15 @@ describe('src/dev/npm/installed_packages', () => {
           licenses: [ 'Apache-2.0' ],
           repository: 'https://github.com/mycorp/dep1',
           directory: resolve(FIXTURE1_ROOT, 'node_modules/dep1'),
-          relative: 'node_modules/dep1',
+          relative: ['node_modules', 'dep1'].join(sep),
         },
         {
           name: 'privatedep',
           version: '0.0.2',
           repository: 'https://github.com/mycorp/privatedep',
           licenses: [ 'Apache-2.0' ],
           directory: resolve(FIXTURE1_ROOT, 'node_modules/privatedep'),
-          relative: 'node_modules/privatedep'
+          relative: ['node_modules', 'privatedep'].join(sep)
         }
       ]);
     });