Add tests for range calc

ui/spec/shared/parsing/getRangeForDygraphSpec.js

@@ -0,0 +1,43 @@
+import getRange from 'shared/parsing/getRangeForDygraph';
+
+describe('getRangeForDygraphSpec', () => {
+  it('gets the range for one timeSeries', () => {
+    const timeSeries = [[new Date(1000), 1], [new Date(2000), 2], [new Date(3000), 3]];
+
+    const actual = getRange(timeSeries);
+    const expected = [1, 3];
+
+    expect(actual).to.deep.equal(expected);
+  });
+
+  it('does not get range when a range is provided', () => {
+    const timeSeries = [[new Date(1000), 1], [new Date(2000), 2], [new Date(3000), 3]];
+
+    const providedRange = [0, 4];
+    const actual = getRange(timeSeries, providedRange);
+
+    expect(actual).to.deep.equal(providedRange);
+  });
+
+  it('gets the range for multiple timeSeries', () => {
+    const timeSeries = [
+      [new Date(1000), null, 1],
+      [new Date(1000), 100, 1],
+      [new Date(2000), null, 2],
+      [new Date(3000), 200, 3],
+    ];
+
+    const actual = getRange(timeSeries);
+    const expected = [1, 200];
+
+    expect(actual).to.deep.equal(expected);
+  });
+
+  it('returns a null array of two elements when min and max are equal', () => {
+    const timeSeries = [[new Date(1000), 1], [new Date(2000), 1], [new Date(3000), 1]];
+    const actual = getRange(timeSeries);
+    const expected = [null, null];
+
+    expect(actual).to.deep.equal(expected);
+  });
+});

ui/src/shared/parsing/getRangeForDygraph.js

@@ -26,7 +26,7 @@ export default function getRange(timeSeries, override, value = null, rangeValue
     [null, pad(rangeValue, "top")],
   ];
 
-  const range = points.reduce(([min, max], series) => {
+  const range = points.reduce(([min, max] = [], series) => {
     for (let i = 1; i < series.length; i++) {
       const val = series[i];