Custom granularity precision should honor 0 if it is passed in closes p…

…rebid#1479 (prebid#1591)

src/cpmBucketManager.js

@@ -88,7 +88,11 @@ function getCpmStringValue(cpm, config, granularityMultiplier) {
   });
   let bucket = config.buckets.find(bucket => {
     if (cpm > cap.max * granularityMultiplier) {
-      const precision = bucket.precision || _defaultPrecision;
+      // cpm exceeds cap, just return the cap.
+      let precision = bucket.precision;
+      if (typeof precision === 'undefined') {
+        precision = _defaultPrecision;
+      }
       cpmStr = (bucket.max * granularityMultiplier).toFixed(precision);
     } else if (cpm <= bucket.max * granularityMultiplier && cpm >= bucket.min * granularityMultiplier) {
       return bucket;
@@ -114,7 +118,7 @@ function isValidPriceConfig(config) {
 }
 
 function getCpmTarget(cpm, increment, precision, granularityMultiplier) {
-  if (!precision) {
+  if (typeof precision === 'undefined') {
     precision = _defaultPrecision;
   }
   let bucketSize = 1 / (increment * granularityMultiplier);

test/spec/cpmBucketManager_spec.js

@@ -58,6 +58,39 @@ describe('cpmBucketManager', () => {
     expect(JSON.stringify(output)).to.deep.equal(expected);
   });
 
+  it('gets custom bucket strings and it should honor 0', () => {
+    let cpm = 16.50908;
+    let customConfig = {
+      'buckets': [
+        {
+          'precision': 0,
+          'min': 3,
+          'max': 18,
+          'increment': 0.05,
+        }
+      ]
+    };
+    let expected = '{"low":"5.00","med":"16.50","high":"16.50","auto":"16.50","dense":"16.50","custom":"17"}';
+    let output = getPriceBucketString(cpm, customConfig);
+    expect(JSON.stringify(output)).to.deep.equal(expected);
+  });
+
+  it('gets the custom bucket strings without passing precision and it should honor the default precision', () => {
+    let cpm = 16.50908;
+    let customConfig = {
+      'buckets': [
+        {
+          'min': 3,
+          'max': 18,
+          'increment': 0.05,
+        }
+      ]
+    };
+    let expected = '{"low":"5.00","med":"16.50","high":"16.50","auto":"16.50","dense":"16.50","custom":"16.50"}';
+    let output = getPriceBucketString(cpm, customConfig);
+    expect(JSON.stringify(output)).to.deep.equal(expected);
+  });
+
   it('checks whether custom config is valid', () => {
     let badConfig = {
       'buckets': [{