Add tests for mesh manifold check

spec/lib/mesh_analysis_spec.rb

@@ -0,0 +1,15 @@
+require "rails_helper"
+
+RSpec.describe "MeshAnalysis" do
+
+  it "verifies that meshes are manifold (i.e. do not have holes)" do
+    geometry = Mittsu::SphereGeometry.new(2.0, 32, 16)
+    expect(geometry.manifold?).to be true
+  end
+
+  it "detects meshes that are non-manifold (i.e. do have holes)" do
+    geometry = Mittsu::PlaneBufferGeometry.new(1.0, 1.0)
+    expect(geometry.manifold?).to be false
+  end
+
+end