edge.isBundledBezier() should return false for styleless instance

- The internal style function, `ele.isBundledBezier()` will not work in a styleless instance, because `ele.pstyle()` will always return `undefined`.  It should have a check like the other style functions.  Most of these functions are derived state functions, which have this check implicitly.
- `edge.isBundledBezier()` is only used in a few places.  The only place that would affect a headless instance is `ele.remove()`.
- This patch includes a fix and several test cases.

Ref : Removing parallel edges in headless mode #2377

src/collection/style.js

@@ -415,6 +415,8 @@ elesfn.hidden = function(){
 };
 
 elesfn.isBundledBezier = cachePrototypeStyleFunction('isBundledBezier', function(){
+  if( !this.cy().styleEnabled() ){ return false; }
+
   return !this.removed() && this.pstyle('curve-style').value === 'bezier' && this.takesUpSpace();
 });
 

test/collection-style.js

@@ -547,6 +547,44 @@ describe('Collection style', function(){
 
       expect( cy.$('#c').visible() ).to.be.true;
     });
+
+    it('ele.isBundledBezier() true for `curve-style: bezier`', function(){
+      var edges = cy.add([
+        { data: { id: 'bez1', source: 'n1', target: 'n2' } },
+        { data: { id: 'bez2', source: 'n1', target: 'n2' } },
+        { data: { id: 'bez3', source: 'n1', target: 'n2' } }
+      ]);
+
+      edges.style('curve-style', 'bezier');
+
+      edges.forEach(function(edge){
+        expect(edge.isBundledBezier(), edge.id()).to.be.true;
+      });
+    });
+
+    it('ele.isBundledBezier() false for style disabled', function(){
+      var cy = cytoscape({
+        headless: true,
+        styleEnabled: false,
+        elements: [
+          { data: { id: 'n1' } },
+          { data: { id: 'n2' } }
+        ]
+      });
+
+      var edges = cy.add([
+        { data: { id: 'bez1', source: 'n1', target: 'n2' } },
+        { data: { id: 'bez2', source: 'n1', target: 'n2' } },
+        { data: { id: 'bez3', source: 'n1', target: 'n2' } }
+      ]);
+
+      // this should be a nop
+      edges.style('curve-style', 'bezier');
+
+      edges.forEach(function(edge){
+        expect(edge.isBundledBezier(), edge.id()).to.be.false;
+      });
+    });
   });
 
   describe('eles.addClass() etc', function(){

test/core-graph-manipulation.js

@@ -172,6 +172,7 @@ describe('Core graph manipulation', function(){
       expect( cy.$('#foo').numericStyle('border-width') ).to.equal(10);
     });
 
+
   });
 
   describe('eles.restore()', function(){
@@ -231,6 +232,42 @@ describe('Core graph manipulation', function(){
 
     });
 
+    it('removes a parallel edge headlessly', function(){
+      // re. headlessly calling edge.isBundledBezier() #2377
+
+      var cy = cytoscape({
+        headless: true,
+        styleEnabled: false, // important
+        elements: [
+          { data: { id: 'a' } },
+          { data: { id: 'b' } },
+          {
+            data: {
+              id: 'ab2',
+              source: 'a',
+              target: 'b'
+            }
+          },
+          {
+            data: {
+              id: 'ab1',
+              source: 'a',
+              target: 'b'
+            }
+          }]
+      });
+
+      cy.edges()[0].remove();
+
+      expect(cy.edges().length, 'number of edges (A)').to.equal(1);
+      expect(cy.nodes().length, 'number of nodes (A)').to.equal(2);
+
+      cy.edges()[0].remove();
+
+      expect(cy.edges().length, 'number of edges (B)').to.equal(0);
+      expect(cy.nodes().length, 'number of nodes (B)').to.equal(2);
+    });
+
     it('removes via selector', function(){
       cy.remove('edge');