diff --git a/spec/lib/mittsu/3mf/exporter_spec.rb b/spec/lib/mittsu/3mf/exporter_spec.rb
new file mode 100644
index 0000000..d1efec0
--- /dev/null
+++ b/spec/lib/mittsu/3mf/exporter_spec.rb
@@ -0,0 +1,62 @@
+require 'rexml/document'
+require 'rexml/xpath'
+
+RSpec.describe Mittsu::ThreeMFExporter do
+  let(:box) {
+    box = Mittsu::Mesh.new(
+      Mittsu::BoxGeometry.new(1.0, 1.0, 1.0)
+    )
+    box.name = "box"
+    box
+  }
+  let (:exporter) { described_class.new }
+
+  it "sanitizes model names for use as filenames" do
+    box.name = "<box>"
+    expect(exporter.send(:filesystem_safe_name, box)).to eq "box"
+  end
+
+  it "can create a valid 3MF model file" do
+    file = exporter.send(:model_file, box)
+    xml = REXML::Document.new file
+    expect(REXML::XPath.first(xml, "/model/@unit").value).to eq "millimeter"
+    expect(REXML::XPath.first(xml, "/model/resources/object/@type").value).to eq "model"
+    expect(REXML::XPath.match(xml, "/model/resources/object/mesh/vertices/vertex").count).to eq 8
+    expect(REXML::XPath.match(xml, "/model/resources/object/mesh/triangles/triangle").count).to eq 12
+  end
+
+  it "exports grouped meshes" do
+    group = Mittsu::Group.new
+    group.add(box)
+    group.add(Mittsu::Mesh.new(Mittsu::SphereGeometry.new()))
+    file = exporter.send(:model_file, group)
+    xml = REXML::Document.new file
+    expect(REXML::XPath.match(xml, "/model/resources/object/mesh").count).to eq 2
+    expect(REXML::XPath.match(xml, "/model/resources/object[1]/mesh/vertices/vertex").count).to eq 8
+    expect(REXML::XPath.match(xml, "/model/resources/object[1]/mesh/triangles/triangle").count).to eq 12
+    expect(REXML::XPath.match(xml, "/model/resources/object[2]/mesh/vertices/vertex").count).to eq 63
+    expect(REXML::XPath.match(xml, "/model/resources/object[2]/mesh/triangles/triangle").count).to eq 88
+    expect(REXML::XPath.match(xml, "/model/build/item").count).to eq 2
+  end
+
+  it "creates a valid content_types file" do
+    file = exporter.send(:content_types_file)
+    xml = REXML::Document.new file
+    expect(REXML::XPath.first(xml, "/Types/Default[@Extension='rels']/@ContentType").value).to eq "application/vnd.openxmlformats-package.relationships+xml"
+  end
+
+  it "creates a valid rels file" do
+    file = exporter.send(:rels_file, ["box"])
+    xml = REXML::Document.new file
+    expect(REXML::XPath.first(xml, "/Relationships/Relationship/@Target").value).to eq "/3D/box.model"
+  end
+
+  it "provides a #parse alias for export, because of API-compatibility with THREE.js" do
+    Dir.mktmpdir do |dir|
+      filename = File.join(dir, "test.3mf")
+      exporter.parse(box, filename)
+      expect(File.exist?(filename)).to be true
+    end
+  end
+
+end
diff --git a/spec/lib/mittsu/3mf/test_exporter.rb b/spec/lib/mittsu/3mf/test_exporter.rb
deleted file mode 100644
index 10b061d..0000000
--- a/spec/lib/mittsu/3mf/test_exporter.rb
+++ /dev/null
@@ -1,65 +0,0 @@
-require 'minitest_helper'
-require 'rexml/document'
-require 'rexml/xpath'
-
-class Test3MFExporter < Minitest::Test
-  def setup
-    @box = Mittsu::Mesh.new(
-      Mittsu::BoxGeometry.new(1.0, 1.0, 1.0)
-    )
-    @box.name = "box"
-    @exporter = Mittsu::ThreeMFExporter.new
-  end
-
-  def test_filename_sanitization
-    @box.name = "<box>"
-    name = @exporter.send(:filesystem_safe_name, @box)
-    assert_equal "box", name
-  end
-
-  def test_3mf_model_file
-    file = @exporter.send(:model_file, @box)
-    xml = REXML::Document.new file
-    assert_equal "millimeter", REXML::XPath.first(xml, "/model/@unit").value
-    assert_equal "model", REXML::XPath.first(xml, "/model/resources/object/@type").value
-    assert_equal 8, REXML::XPath.match(xml, "/model/resources/object/mesh/vertices/vertex").count
-    assert_equal 12, REXML::XPath.match(xml, "/model/resources/object/mesh/triangles/triangle").count
-  end
-
-  def test_grouped_meshes
-    group = Mittsu::Group.new
-    group.add(@box)
-    group.add(Mittsu::Mesh.new(Mittsu::SphereGeometry.new()))
-    file = @exporter.send(:model_file, group)
-    xml = REXML::Document.new file
-    assert_equal 2, REXML::XPath.match(xml, "/model/resources/object/mesh").count
-    assert_equal 8, REXML::XPath.match(xml, "/model/resources/object[1]/mesh/vertices/vertex").count
-    assert_equal 12, REXML::XPath.match(xml, "/model/resources/object[1]/mesh/triangles/triangle").count
-    assert_equal 63, REXML::XPath.match(xml, "/model/resources/object[2]/mesh/vertices/vertex").count
-    assert_equal 88, REXML::XPath.match(xml, "/model/resources/object[2]/mesh/triangles/triangle").count
-    assert_equal 2, REXML::XPath.match(xml, "/model/build/item").count
-  end
-
-  def test_content_types_file
-    file = @exporter.send(:content_types_file)
-    xml = REXML::Document.new file
-    assert_equal "application/vnd.openxmlformats-package.relationships+xml",
-      REXML::XPath.first(xml, "/Types/Default[@Extension='rels']/@ContentType").value
-  end
-
-  def test_rels_file
-    file = @exporter.send(:rels_file, ["box"])
-    xml = REXML::Document.new file
-    assert_equal "/3D/box.model",
-      REXML::XPath.first(xml, "/Relationships/Relationship/@Target").value
-  end
-
-  def test_export_method_alias
-    Dir.mktmpdir do |dir|
-      filename = File.join(dir, "test.3mf")
-      @exporter.parse(@box, filename)
-      assert File.exist?(filename)
-    end
-  end
-
-end