diff --git a/src/index.ts b/src/index.ts
index 94e7652..4725c19 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,10 +1,10 @@
 import { app } from './server';
-import { updateData, startPeriodicUpdates } from './utils/data_fetcher';
+import { updateData, startPeriodicallyCalling } from './utils/data_fetcher';
 
 updateData();
 const default_interval: string = (1000 * 60 * 60 * 24).toString();
 const interval: string = process.env["UPDATE_INTERVAL"] || default_interval;
-startPeriodicUpdates(parseInt(interval));
+startPeriodicallyCalling(updateData, parseInt(interval));
 
 const PORT = process.env.PORT || 3000;
 
diff --git a/src/utils/__tests__/test_data_fetcher.ts b/src/utils/__tests__/test_data_fetcher.ts
new file mode 100644
index 0000000..7b9b2d1
--- /dev/null
+++ b/src/utils/__tests__/test_data_fetcher.ts
@@ -0,0 +1,19 @@
+import {startPeriodicallyCalling} from "../data_fetcher";
+
+describe("Data updating functions", () => {
+
+    it("should update once for each period", () => {
+        let updateData = jest.fn();
+        startPeriodicallyCalling(updateData, 300, new Date());
+        setTimeout(() => expect(updateData).toHaveBeenCalledTimes(3), 1000);
+    });
+
+    it("should only start updating after the start date", () => {
+        let updateData = jest.fn();
+        const startDate = new Date();
+        startDate.setMilliseconds(startDate.getMilliseconds() + 500);
+        startPeriodicallyCalling(updateData, 200, startDate);
+        setTimeout(() => expect(updateData).toHaveBeenCalledTimes(0), 400);
+        setTimeout(() => expect(updateData).toHaveBeenCalledTimes(2), 1000);
+    });
+});
diff --git a/src/utils/data_fetcher.ts b/src/utils/data_fetcher.ts
index a781d31..278d876 100644
--- a/src/utils/data_fetcher.ts
+++ b/src/utils/data_fetcher.ts
@@ -4,26 +4,35 @@ let mostRecentGeneMap: GeneMap;
 let mostRecentAnnotations: IAnnotation[];
 let mostRecentGroupedAnnotations: GroupedAnnotations<Set<IGene>>;
 
-export const updateData = () => {
+export const getGeneMap = (): GeneMap => { return mostRecentGeneMap; };
+
+export const getAnnotations = (): IAnnotation[] => { return mostRecentAnnotations; };
+
+export const getGroupedAnnotations = (): GroupedAnnotations<Set<IGene>> => { return mostRecentGroupedAnnotations; };
+
+export const downloadData = (dataUrl: string = "http://current.geneontology.org/annotations/tair.gaf.gz") => {
     const { execSync } = require("child_process");
-    const stdout = execSync("wget http://current.geneontology.org/annotations/tair.gaf.gz ; gunzip tair.gaf.gz");
+    const stdout = execSync("wget " + dataUrl + " ; gunzip tair.gaf.gz");
+}
 
+export const updateData = () => {
+    downloadData();
     const { geneMap, annotations, groupedAnnotations } = readData();
     mostRecentGeneMap = geneMap;
     mostRecentAnnotations = annotations;
     mostRecentGroupedAnnotations = groupedAnnotations;
 };
 
-export const startPeriodicUpdates = (interval: number = (1000 * 60 * 60 * 24), startDate: Date = getTomorrowMorning()) => {
+export const startPeriodicallyCalling = (fn: (...args: any[]) => void, interval: number = (1000 * 60 * 60 * 24), startDate: Date = getTomorrowMorning()) => {
     const now = new Date();
-    if (sameTimeOfDay(startDate, now)) {
-        setInterval(updateData, interval);
+    if (isSameTimeOfDay(startDate, now)) {
+        setInterval(fn, interval);
     } else {
         let difference = startDate.getTime() - now.getTime();
         if (difference > 0) {
-            setTimeout(startPeriodicUpdates, difference, interval, startDate);
+            setTimeout(startPeriodicallyCalling, difference, fn, interval, startDate);
         }
-        setInterval(updateData, interval);  // Just begins the updates now if the startDate is in the past
+        setInterval(fn, interval);  // Just begins the updates now if the startDate is in the past
     }
 };
 
@@ -36,12 +45,6 @@ const getTomorrowMorning = (): Date => {
     return tomorrowMorning;
 };
 
-const sameTimeOfDay = (time1, time2) => {
+const isSameTimeOfDay = (time1, time2) => {
     return time1.getHours() === time2.getHours() && time1.getMinutes() === time2.getMinutes();
 }
-
-export const getGeneMap = (): GeneMap => { return mostRecentGeneMap; };
-
-export const getAnnotations = (): IAnnotation[] => { return mostRecentAnnotations; };
-
-export const getGroupedAnnotations = (): GroupedAnnotations<Set<IGene>> => { return mostRecentGroupedAnnotations; };