diff --git a/modules/core/data.js b/modules/core/data.js
index 0a89cb0a0..e244ca216 100644
--- a/modules/core/data.js
+++ b/modules/core/data.js
@@ -2,46 +2,58 @@ import { json as d3_json } from 'd3-fetch';
 import { data as _data } from '../../data';  // prebundled data
 
 
-let _inflight = {};
-
-const FILES = {
-  'intro_graph': 'data/intro_graph.json'
-};
-
-
+//
+// The coreData module fetches data from JSON files
+//
 export function coreData(context) {
+  let _module = {};
+  let _inflight = {};
+  let _fileMap = {
+    'intro_graph': 'data/intro_graph.json'
+  };
 
-  return {
-    get: (which) => {
-      if (_data[which]) {
-        return Promise.resolve(_data[which]);
-      }
 
-      const file = FILES[which];
-      const url = file && context.asset(file);
-      if (!url) {
-        return Promise.reject(`Unknown data file for "${which}"`);
-      }
-
-      let prom = _inflight[url];
-      if (!prom) {
-        _inflight[url] = prom = d3_json(url)
-          .then(result => {
-            delete _inflight[url];
-            if (!result) {
-              throw new Error(`No data loaded for "${which}"`);
-            }
-            _data[which] = result;
-            return result;
-          })
-          .catch(err => {
-            delete _inflight[url];
-            throw err;
-          });
-      }
-
-      return prom;
+  // Returns a Promise to fetch data
+  // (resolved with the data if we have it already)
+  _module.get = (which) => {
+    if (_data[which]) {
+      return Promise.resolve(_data[which]);
     }
 
+    const file = _fileMap[which];
+    const url = file && context.asset(file);
+    if (!url) {
+      return Promise.reject(`Unknown data file for "${which}"`);
+    }
+
+    let prom = _inflight[url];
+    if (!prom) {
+      _inflight[url] = prom = d3_json(url)
+        .then(result => {
+          delete _inflight[url];
+          if (!result) {
+            throw new Error(`No data loaded for "${which}"`);
+          }
+          _data[which] = result;
+          return result;
+        })
+        .catch(err => {
+          delete _inflight[url];
+          throw err;
+        });
+    }
+
+    return prom;
   };
+
+
+  // Accessor for the file map
+  _module.fileMap = function(val) {
+    if (!arguments.length) return _fileMap;
+    _fileMap = val;
+    return _module;
+  };
+
+
+  return _module;
 }
diff --git a/test/data/intro_graph.json b/test/data/intro_graph.json
new file mode 100644
index 000000000..d73b65096
--- /dev/null
+++ b/test/data/intro_graph.json
@@ -0,0 +1,15 @@
+{
+  "n1": {
+    "id": "n1",
+    "loc": [-85.636433, 41.942959],
+    "tags": {
+      "addr:city": "Three Rivers",
+      "addr:housenumber": "333",
+      "addr:postcode": "49093",
+      "addr:state": "MI",
+      "addr:street": "Michigan Avenue",
+      "amenity": "townhall",
+      "name": "Three Rivers City Hall"
+    }
+  }
+}
diff --git a/test/index.html b/test/index.html
index 7ea279990..6c5640719 100644
--- a/test/index.html
+++ b/test/index.html
@@ -71,6 +71,7 @@
   <script src='spec/behavior/lasso.js'></script>
 
   <script src='spec/core/context.js'></script>
+  <script src='spec/core/data.js'></script>
   <script src='spec/core/difference.js'></script>
   <script src='spec/core/graph.js'></script>
   <script src='spec/core/history.js'></script>
diff --git a/test/spec/core/data.js b/test/spec/core/data.js
new file mode 100644
index 000000000..908b812c4
--- /dev/null
+++ b/test/spec/core/data.js
@@ -0,0 +1,62 @@
+describe('iD.coreData', function() {
+    var _context;
+    var _oldData;
+
+    before(function() {
+        iD.data.test = { hello: 'world' };
+    });
+
+    after(function() {
+        delete iD.data.test;
+    });
+
+    beforeEach(function() {
+        _context = iD.coreContext();
+    });
+
+
+    describe('#fileMap', function() {
+        it('gets the fileMap', function() {
+            var data = iD.coreData(_context);
+            expect(data.fileMap()).to.be.a('object');
+        });
+        it('sets the fileMap', function() {
+            var data = iD.coreData(_context);
+            var files = { 'intro_graph': 'data/intro_graph.json' };
+            expect(data.fileMap(files)).to.be.ok;
+        });
+    });
+
+    describe('#get', function() {
+        it('returns a promise resolved if we already have the data', function(done) {
+            var data = iD.coreData(_context);
+            var prom = data.get('test');
+            expect(prom).to.be.a('promise');
+            prom.then(function (data) {
+                expect(data).to.be.a('object');
+                expect(data.hello).to.eql('world');
+                done();
+            });
+        });
+        it('returns a promise rejected if we can not get the data', function(done) {
+            var data = iD.coreData(_context);
+            var prom = data.get('wat');
+            prom.catch(function (err) {
+                expect(/^Unknown data file/.test(err)).to.be.true;
+                done();
+            });
+        });
+        it('returns a promise to fetch data if we do not already have the data', function(done) {
+            var files = { 'intro_graph': 'data/intro_graph.json' };
+            var data = iD.coreData(_context).fileMap(files);
+            var prom = data.get('intro_graph');
+            expect(prom).to.be.a('promise');
+            prom.then(function (data) {
+                expect(data).to.be.a('object');
+                expect(data.n1.tags.name).to.eql('Three Rivers City Hall');
+                done();
+            });
+        });
+    });
+
+});