diff --git a/test/factories/note_tags.rb b/test/factories/note_tags.rb
new file mode 100644
index 0000000000..f7d90e002d
--- /dev/null
+++ b/test/factories/note_tags.rb
@@ -0,0 +1,8 @@
+FactoryBot.define do
+  factory :note_tag do
+    sequence(:k) { |n| "Key #{n}" }
+    sequence(:v) { |n| "Value #{n}" }
+
+    note
+  end
+end
diff --git a/test/models/note_tag_test.rb b/test/models/note_tag_test.rb
index 35a3087b86..058d68eb87 100644
--- a/test/models/note_tag_test.rb
+++ b/test/models/note_tag_test.rb
@@ -1,7 +1,49 @@
 require "test_helper"
 
 class NoteTagTest < ActiveSupport::TestCase
-  # test "the truth" do
-  #   assert true
-  # end
+  def test_length_key_valid
+    tag = create(:note_tag)
+    [0, 255].each do |i|
+      tag.k = "k" * i
+      assert_predicate tag, :valid?
+    end
+  end
+
+  def test_length_value_valid
+    tag = create(:note_tag)
+    [0, 255].each do |i|
+      tag.v = "v" * i
+      assert_predicate tag, :valid?
+    end
+  end
+
+  def test_length_key_invalid
+    tag = create(:note_tag)
+    tag.k = "k" * 256
+    assert_not_predicate tag, :valid?, "Key should be too long"
+    assert_predicate tag.errors[:k], :any?
+  end
+
+  def test_length_value_invalid
+    tag = create(:note_tag)
+    tag.v = "v" * 256
+    assert_not_predicate tag, :valid?, "Value should be too long"
+    assert_predicate tag.errors[:v], :any?
+  end
+
+  def test_orphaned_tag_invalid
+    tag = create(:note_tag)
+    tag.note = nil
+    assert_not_predicate tag, :valid?, "Orphaned tag should be invalid"
+    assert_predicate tag.errors[:note], :any?
+  end
+
+  def test_uniqueness
+    existing = create(:note_tag)
+    tag = build(:note_tag, :note => existing.note, :k => existing.k, :v => existing.v)
+    assert_predicate tag, :new_record?
+    assert_not_predicate tag, :valid?
+    assert_raise(ActiveRecord::RecordInvalid) { tag.save! }
+    assert_predicate tag, :new_record?
+  end
 end