fix(dvb): correct off-by-one in DVBSelector weighted BaseURL selection

Remove erroneous `- 1` in random number generation that shrank the
selection range, causing the last BaseURL in a weighted group to never
be selected. With 2 equal-weight CDNs, only the first was ever picked.

Also add stub.restore() to existing DVB A168 test to prevent sinon
stub leak, and add two unit tests for equal-weight selection (2 and 3
CDNs).

Fixes Dash-Industry-Forum#4981

Author: PascalThuet

src/streaming/utils/baseUrlResolution/DVBSelector.js

@@ -111,7 +111,7 @@ function DVBSelector(config) {
                 });
 
                 // pick a random number between zero and totalWeight
-                rn = Math.floor(Math.random() * (totalWeight - 1));
+                rn = Math.floor(Math.random() * totalWeight);
 
                 // select the index for the range rn falls within
                 cumulWeights.every((limit, index) => {

test/unit/test/streaming/streaming.utils.DVBSelector.js

@@ -154,6 +154,63 @@ describe('BaseURLResolution/DVBSelector', function () {
 
         const fourthSelection = dvbSelector.select(baseUrls);
         expect(fourthSelection).to.be.undefined;
+
+        stub.restore();
+    });
+
+    it('should select all equal-weight baseUrls with fair distribution (RFC 2782)', () => {
+        const baseUrls = [
+            { dvbPriority: 1, dvbWeight: 1, serviceLocation: 'cdn-a' },
+            { dvbPriority: 1, dvbWeight: 1, serviceLocation: 'cdn-b' }
+        ];
+
+        const stub = sinon.stub(Math, 'random');
+        const dvbSelector = DVBSelector(context).create(defaultConfig);
+
+        // With totalWeight=2 and cumulWeights=[1,2]:
+        // Math.random()=0.0 → rn=0 → 0<1 → cdn-a
+        stub.returns(0.0);
+        expect(dvbSelector.select(baseUrls).serviceLocation).to.equal('cdn-a');
+
+        // Math.random()=0.4 → rn=0 → 0<1 → cdn-a
+        stub.returns(0.4);
+        expect(dvbSelector.select(baseUrls).serviceLocation).to.equal('cdn-a');
+
+        // Math.random()=0.5 → rn=1 → 1<2 → cdn-b
+        stub.returns(0.5);
+        expect(dvbSelector.select(baseUrls).serviceLocation).to.equal('cdn-b');
+
+        // Math.random()=0.99 → rn=1 → 1<2 → cdn-b
+        stub.returns(0.99);
+        expect(dvbSelector.select(baseUrls).serviceLocation).to.equal('cdn-b');
+
+        stub.restore();
+    });
+
+    it('should select all three equal-weight baseUrls (multi-CDN without dvb:weight)', () => {
+        const baseUrls = [
+            { dvbPriority: 1, dvbWeight: 1, serviceLocation: 'cdn-a' },
+            { dvbPriority: 1, dvbWeight: 1, serviceLocation: 'cdn-b' },
+            { dvbPriority: 1, dvbWeight: 1, serviceLocation: 'cdn-c' }
+        ];
+
+        const stub = sinon.stub(Math, 'random');
+        const dvbSelector = DVBSelector(context).create(defaultConfig);
+
+        // With totalWeight=3 and cumulWeights=[1,2,3]:
+        // Math.random()=0.0 → rn=0 → 0<1 → cdn-a
+        stub.returns(0.0);
+        expect(dvbSelector.select(baseUrls).serviceLocation).to.equal('cdn-a');
+
+        // Math.random()=0.5 → rn=1 → 1<2 → cdn-b
+        stub.returns(0.5);
+        expect(dvbSelector.select(baseUrls).serviceLocation).to.equal('cdn-b');
+
+        // Math.random()=0.8 → rn=2 → 2<3 → cdn-c
+        stub.returns(0.8);
+        expect(dvbSelector.select(baseUrls).serviceLocation).to.equal('cdn-c');
+
+        stub.restore();
     });
 
     it('should not select baseUrls with invalid priority when there is another option', () => {