diff --git a/index.d.ts b/index.d.ts
index c749ecb5..714ab6b9 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -69,6 +69,30 @@ interface TSMLReactConfig {
 
 declare var tsml_react_config: Readonly<TSMLReactConfig> | undefined;
 
+//google analytics globals
+declare var gtag:
+  | ((
+      type: 'event',
+      action: string,
+      params: {
+        event_category: string;
+        event_label: string;
+      }
+    ) => void)
+  | undefined;
+
+declare var ga:
+  | ((
+      type: 'send',
+      params: {
+        hitType: 'event';
+        eventCategory: string;
+        eventAction: string;
+        eventLabel: string;
+      }
+    ) => void)
+  | undefined;
+
 //declaration merge for IE compat
 interface Navigator {
   msSaveBlob: (blob: Blob, name: string) => void;
diff --git a/src/helpers/analytics.spec.ts b/src/helpers/analytics.spec.ts
new file mode 100644
index 00000000..e69f0cca
--- /dev/null
+++ b/src/helpers/analytics.spec.ts
@@ -0,0 +1,28 @@
+import { analyticsEvent } from '.';
+
+window.gtag = jest.fn();
+window.ga = jest.fn();
+
+describe('analytics', () => {
+  it('calls gtag if defined', () => {
+    analyticsEvent({ action: 'foo', category: 'bar', label: 'baz' });
+
+    expect(gtag).toHaveBeenCalledWith('event', 'foo', {
+      event_category: 'bar',
+      event_label: 'baz',
+    });
+  });
+
+  it('calls ga if defined when gtag is undefined', () => {
+    window.gtag = undefined;
+
+    analyticsEvent({ action: 'foo', category: 'bar', label: 'baz' });
+
+    expect(ga).toHaveBeenCalledWith('send', {
+      eventAction: 'foo',
+      eventCategory: 'bar',
+      eventLabel: 'baz',
+      hitType: 'event',
+    });
+  });
+});
diff --git a/src/helpers/distance.js b/src/helpers/distance.js
index 26cb34c8..b4825130 100644
--- a/src/helpers/distance.js
+++ b/src/helpers/distance.js
@@ -17,6 +17,7 @@ export function distance(a, b) {
       Math.sin(aRadLat) * Math.sin(bRadLat) +
       Math.cos(aRadLat) * Math.cos(bRadLat) * Math.cos(radTheta);
 
+    // TODO: How to test the scenario for this line?
     if (dist > 1) dist = 1;
 
     dist = Math.acos(dist);
diff --git a/src/helpers/distance.spec.ts b/src/helpers/distance.spec.ts
new file mode 100644
index 00000000..99d4753c
--- /dev/null
+++ b/src/helpers/distance.spec.ts
@@ -0,0 +1,52 @@
+import { distance } from './distance';
+import { settings } from './settings';
+
+jest.mock('./settings', () => ({
+  settings: { distance_unit: 'mi' },
+}));
+
+describe('distance', () => {
+  //exact
+  it('returns 0 for exact location', () => {
+    const obj = { latitude: 1, longitude: 1 };
+    expect(distance(obj, obj)).toStrictEqual(0);
+  });
+
+  //miles
+  it.each`
+    a                                    | b                                    | expected
+    ${{ latitude: 1, longitude: 1 }}     | ${{ latitude: 2, longitude: 2 }}     | ${97.69}
+    ${{ latitude: 10, longitude: 10 }}   | ${{ latitude: 20, longitude: 20 }}   | ${959.82}
+    ${{ latitude: 100, longitude: 100 }} | ${{ latitude: 200, longitude: 200 }} | ${7697.83}
+  `('miles: yields $expected with $a and $b', ({ a, b, expected }) => {
+    expect(distance(a, b)).toStrictEqual(expected);
+  });
+
+  //kilometers
+  it.each`
+    a                                    | b                                    | expected
+    ${{ latitude: 1, longitude: 1 }}     | ${{ latitude: 2, longitude: 2 }}     | ${157.22}
+    ${{ latitude: 10, longitude: 10 }}   | ${{ latitude: 20, longitude: 20 }}   | ${1544.68}
+    ${{ latitude: 100, longitude: 100 }} | ${{ latitude: 200, longitude: 200 }} | ${12388.45}
+  `('kilometers: yields $expected with $a and $b', ({ a, b, expected }) => {
+    settings.distance_unit = 'km';
+    expect(distance(a, b)).toStrictEqual(expected);
+  });
+
+  //null checks
+  it.each`
+    a                                | b
+    ${null}                          | ${null}
+    ${{ latitude: 1 }}               | ${null}
+    ${{ longitude: 1 }}              | ${null}
+    ${{ latitude: 1, longitude: 1 }} | ${null}
+    ${null}                          | ${{ latitude: 1 }}
+    ${null}                          | ${{ longitude: 1 }}
+    ${null}                          | ${{ latitude: 1, longitude: 1 }}
+    ${{ latitude: 1 }}               | ${{ latitude: 1 }}
+    ${{ latitude: 1, longitude: 1 }} | ${{ latitude: 1 }}
+    ${{ latitude: 1 }}               | ${{ latitude: 1, longitude: 1 }}
+  `('yields null with $a and $b', ({ a, b }) => {
+    expect(distance(a, b)).toStrictEqual(null);
+  });
+});