Added .getReferenceTarget

spec/git-repository-async-spec.js

@@ -485,4 +485,17 @@ describe('GitRepositoryAsync', () => {
       expect(tags.length).toBe(0)
     })
   })
+
+  describe('.getReferenceTarget(reference, path)', () => {
+    let workingDirectory
+    beforeEach(() => {
+      workingDirectory = copyRepository()
+      repo = GitRepositoryAsync.open(workingDirectory)
+    })
+
+    it('returns the SHA target', async () => {
+      const SHA = await repo.getReferenceTarget('refs/heads/master')
+      expect(SHA).toBe('8a9c86f1cb1f14b8f436eb91f4b052c8802ca99e')
+    })
+  })
 })

src/git-repository-async.js

@@ -288,13 +288,18 @@ export default class GitRepositoryAsync {
       })
   }
 
-  // Public: Returns the current {String} SHA for the given reference.
+  // Public: Get the SHA for the given reference.
   //
   // * `reference` The {String} reference to get the target of.
   // * `path` An optional {String} path in the repo to get the reference target
   //   for. Only needed if the repository contains submodules.
+  //
+  // Returns a {Promise} which resolves to the current {String} SHA for the
+  // given reference.
   getReferenceTarget (reference, _path) {
-    throw new Error('Unimplemented')
+    return this._getRepo(_path)
+      .then(repo => repo.getReference(reference))
+      .then(ref => ref.target().tostrS())
   }
 
   // Reading Status