Make testing environment with bug repro code

examples3d/spherical_joint_testing.rs

@@ -0,0 +1,38 @@
+use rapier3d::prelude::*;
+use rapier_testbed3d::{Testbed, TestbedApp};
+
+pub fn init_world(testbed: &mut Testbed) {
+
+    let mut bodies = RigidBodySet::new();
+    let mut colliders = ColliderSet::new();
+    let impulse_joints = ImpulseJointSet::new();
+    let mut multibody_joints = MultibodyJointSet::new();
+
+
+    let ground = RigidBodyBuilder::fixed().translation(vector![0.0, 0.0, 0.0]);
+    let body = bodies.insert(ground);
+    let collider = ColliderBuilder::cuboid(1.0, 1.0, 1.0);
+    colliders.insert_with_parent(collider, body, &mut bodies);
+
+
+    let rigid_body = RigidBodyBuilder::dynamic().position(Isometry::translation(0.0, 1.0, 0.0));
+    let body_part = bodies.insert(rigid_body);
+    let collider = ColliderBuilder::cuboid(1.0, 1.0, 1.0).density(1.0);
+    colliders.insert_with_parent(collider, body_part, &mut bodies);
+
+
+    let joint = SphericalJointBuilder::new()
+        .local_anchor1(point![0.0, 4.0, 0.0])
+        .local_anchor2(point![0.0, 0.0, 0.0])
+
+        .motor_position(JointAxis::AngX, 1.0, 1000.0, 200.0)
+        .motor_position(JointAxis::AngY, 0.0, 1000.0, 200.0)
+        .motor_position(JointAxis::AngZ, 0.0, 1000.0, 200.0);
+
+
+    multibody_joints.insert(body, body_part, joint, true);
+
+
+    testbed.set_world(bodies, colliders, impulse_joints, multibody_joints);
+    testbed.look_at(point![20.0, 0.0, 0.0], point![0.0, 0.0, 0.0]);
+}