Register enable/disable flag test

I decided to use a global flag to manage the enabled/disabled state of the registers used to store shader attributes.
This value will be true if the geometry supplies a value, false if it does not.
Therefore, I prepared a geometry with aTexCoord and a geometry without it, and tested whether the value was properly switched.

test/unit/webgl/p5.RendererGL.js

@@ -1392,6 +1392,44 @@ suite('p5.RendererGL', function() {
     });
   });
 
+  suite('Test for register availability', function() {
+    test('register enable/disable flag test', function(done) {
+      const renderer = myp5.createCanvas(16, 16, myp5.WEBGL);
+
+      // geometry without aTexCoord.
+      const myGeom = new p5.Geometry(1, 1, function() {
+        this.gid = 'registerEnabledTest';
+        this.vertices.push(createVector(-8, -8));
+        this.vertices.push(createVector(8, -8));
+        this.vertices.push(createVector(8, 8));
+        this.vertices.push(createVector(-8, 8));
+        this.faces.push([0, 1, 2]);
+        this.faces.push([0, 2, 3]);
+        this.computeNormals();
+      });
+
+      myp5.fill(255);
+      myp5.directionalLight(255, 255, 255, 0, 0, -1);
+
+      myp5.triangle(-8, -8, 8, -8, 8, 8);
+
+      // get register location of
+      // lightingShader's aTexCoord attribute.
+      const attributes = renderer._curShader.attributes;
+      const loc = attributes.aTexCoord.location;
+
+      assert.equal(renderer.registerEnabled[loc], true);
+
+      myp5.model(myGeom);
+      assert.equal(renderer.registerEnabled[loc], false);
+
+      myp5.triangle(-8, -8, 8, 8, -8, 8);
+      assert.equal(renderer.registerEnabled[loc], true);
+
+      done();
+    });
+  });
+
   suite('setAttributes', function() {
     test('It leaves a reference to the correct canvas', function(done) {
       const renderer = myp5.createCanvas(10, 10, myp5.WEBGL);