diff --git a/test/controllers/splits_controller_test.rb b/test/controllers/splits_controller_test.rb
index 5cb89a9ff..412ef7aef 100644
--- a/test/controllers/splits_controller_test.rb
+++ b/test/controllers/splits_controller_test.rb
@@ -17,6 +17,21 @@ class SplitsControllerTest < ActionDispatch::IntegrationTest
     assert_response :success
   end
 
+  test "new groups subcategories immediately after their parent in the category selector" do
+    get new_transaction_split_path(@entry)
+    assert_response :success
+
+    doc = Nokogiri::HTML::Document.parse(response.body)
+    category_values = doc.css(".category-select-container [data-value]").map { |node| node["data-value"] }
+
+    parent_index = category_values.index(categories(:food_and_drink).id)
+    child_index = category_values.index(categories(:subcategory).id)
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index
+  end
+
   test "create with valid params splits transaction" do
     assert_difference "Entry.count", 2 do
       post transaction_split_path(@entry), params: {
diff --git a/test/controllers/transactions/categorizes_controller_test.rb b/test/controllers/transactions/categorizes_controller_test.rb
index 1e74d8bbb..8c40f3286 100644
--- a/test/controllers/transactions/categorizes_controller_test.rb
+++ b/test/controllers/transactions/categorizes_controller_test.rb
@@ -26,6 +26,23 @@ class Transactions::CategorizesControllerTest < ActionDispatch::IntegrationTest
     assert_response :success
   end
 
+  test "show groups subcategories immediately after their parent in the category select" do
+    create_transaction(account: @account, name: "Starbucks")
+    get transactions_categorize_url
+
+    assert_response :success
+
+    doc = Nokogiri::HTML::Document.parse(response.body)
+    option_values = doc.css("select[name='category_id'] option").map { |node| node["value"] }
+
+    parent_index = option_values.index(categories(:food_and_drink).id)
+    child_index = option_values.index(categories(:subcategory).id)
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index
+  end
+
   test "show renders full dates so multi-year lists are unambiguous" do
     create_transaction(account: @account, name: "Starbucks", date: Date.new(2024, 7, 8))
 
diff --git a/test/controllers/transactions_controller_test.rb b/test/controllers/transactions_controller_test.rb
index b533d89c7..0be05a1af 100644
--- a/test/controllers/transactions_controller_test.rb
+++ b/test/controllers/transactions_controller_test.rb
@@ -8,6 +8,21 @@ class TransactionsControllerTest < ActionDispatch::IntegrationTest
     @entry = entries(:transaction)
   end
 
+  test "index groups subcategories immediately after their parent in the category filter" do
+    get transactions_url
+    assert_response :success
+
+    doc = Nokogiri::HTML::Document.parse(response.body)
+    checkbox_values = doc.css("input[name='q[categories][]']").map { |node| node["value"] }
+
+    parent_index = checkbox_values.index(categories(:food_and_drink).name)
+    child_index = checkbox_values.index(categories(:subcategory).name)
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index
+  end
+
   test "creates with transaction details" do
     assert_difference [ "Entry.count", "Transaction.count" ], 1 do
       post transactions_url, params: {
@@ -467,6 +482,37 @@ end
     assert_not entry.protected_from_sync?
   end
 
+  test "new groups subcategories immediately after their parent in the category select" do
+    get new_transaction_url
+    assert_response :success
+
+    doc = Nokogiri::HTML::Document.parse(response.body)
+    trigger = doc.at_css("#category_id_trigger")
+    assert_not_nil trigger, "expected the category select trigger button to render"
+
+    wrapper = trigger.ancestors(".relative").first
+    category_values = wrapper.css("[data-value]").map { |node| node["data-value"] }
+
+    parent_index = category_values.index(categories(:food_and_drink).id)
+    child_index = category_values.index(categories(:subcategory).id)
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index
+  end
+
+  test "new renders a search box for account selection" do
+    get new_transaction_url
+    assert_response :success
+
+    doc = Nokogiri::HTML::Document.parse(response.body)
+    trigger = doc.at_css("#account_id_trigger")
+    assert_not_nil trigger, "expected the account select trigger button to render"
+
+    wrapper = trigger.ancestors(".relative").first
+    assert_not_nil wrapper.at_css("input[type='search']"), "expected a search input inside the account select"
+  end
+
   test "new with duplicate_entry_id pre-fills form from source transaction" do
     @entry.reload
 
diff --git a/test/models/category/group_test.rb b/test/models/category/group_test.rb
new file mode 100644
index 000000000..cfe366e3e
--- /dev/null
+++ b/test/models/category/group_test.rb
@@ -0,0 +1,52 @@
+require "test_helper"
+
+class Category::GroupTest < ActiveSupport::TestCase
+  setup do
+    @family = families(:dylan_family)
+  end
+
+  test "for groups categories by parent, root categories without children get an empty subcategories array" do
+    groups = Category::Group.for(@family.categories)
+
+    food_group = groups.find { |g| g.category == categories(:food_and_drink) }
+    assert_equal [ categories(:subcategory) ], food_group.subcategories
+
+    income_group = groups.find { |g| g.category == categories(:income) }
+    assert_equal [], income_group.subcategories
+  end
+
+  test "for does not include a category as its own root when it is a subcategory" do
+    groups = Category::Group.for(@family.categories)
+
+    assert_nil groups.find { |g| g.category == categories(:subcategory) }
+  end
+
+  test "select_options orders parent immediately followed by its children" do
+    options = Category::Group.select_options(@family.categories)
+
+    parent_index = options.index { |label, id| id == categories(:food_and_drink).id }
+    child_index = options.index { |label, id| id == categories(:subcategory).id }
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index, "subcategory should immediately follow its parent in the options list"
+  end
+
+  test "select_options indents subcategory labels so they're visually distinguishable from parents" do
+    options = Category::Group.select_options(@family.categories)
+
+    parent_label, = options.find { |label, id| id == categories(:food_and_drink).id }
+    child_label, = options.find { |label, id| id == categories(:subcategory).id }
+
+    assert_equal categories(:food_and_drink).name, parent_label
+    assert_not_equal categories(:subcategory).name, child_label
+    assert_includes child_label, categories(:subcategory).name
+  end
+
+  test "select_options returns [label, id] pairs usable directly by options_for_select / form.select" do
+    options = Category::Group.select_options(@family.categories)
+
+    assert options.all? { |pair| pair.is_a?(Array) && pair.size == 2 }
+    assert options.all? { |_label, id| id.present? }
+  end
+end
diff --git a/test/models/category_test.rb b/test/models/category_test.rb
index a12b9790a..7ef173b11 100644
--- a/test/models/category_test.rb
+++ b/test/models/category_test.rb
@@ -159,4 +159,15 @@ class CategoryTest < ActiveSupport::TestCase
     assert lookup.key?(category.id)
     assert_not lookup.key?(0)
   end
+
+  test "alphabetically_by_hierarchy orders a category's subcategories immediately after it" do
+    ordered = @family.categories.alphabetically_by_hierarchy.to_a
+
+    parent_index = ordered.index(categories(:food_and_drink))
+    child_index = ordered.index(categories(:subcategory))
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index
+  end
 end
diff --git a/test/models/import/category_mapping_test.rb b/test/models/import/category_mapping_test.rb
new file mode 100644
index 000000000..4d20966b1
--- /dev/null
+++ b/test/models/import/category_mapping_test.rb
@@ -0,0 +1,25 @@
+require "test_helper"
+
+class Import::CategoryMappingTest < ActiveSupport::TestCase
+  setup do
+    @mapping = import_mappings(:one)
+  end
+
+  test "selectable_values groups subcategories immediately after their parent" do
+    options = @mapping.selectable_values
+
+    parent_index = options.index { |_label, id| id == categories(:food_and_drink).id }
+    child_index = options.index { |_label, id| id == categories(:subcategory).id }
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index
+  end
+
+  test "selectable_values still prepends 'Add as new category' when key is present" do
+    options = @mapping.selectable_values
+
+    assert_equal "Add as new category", options.first.first
+    assert_equal Import::Mapping::CREATE_NEW_KEY, options.first.last
+  end
+end
diff --git a/test/models/rule/action_executor/set_transaction_category_test.rb b/test/models/rule/action_executor/set_transaction_category_test.rb
new file mode 100644
index 000000000..404a93198
--- /dev/null
+++ b/test/models/rule/action_executor/set_transaction_category_test.rb
@@ -0,0 +1,19 @@
+require "test_helper"
+
+class Rule::ActionExecutor::SetTransactionCategoryTest < ActiveSupport::TestCase
+  setup do
+    @rule = rules(:one)
+    @executor = Rule::ActionExecutor::SetTransactionCategory.new(@rule)
+  end
+
+  test "options groups subcategories immediately after their parent" do
+    options = @executor.options
+
+    parent_index = options.index { |_label, id| id == categories(:food_and_drink).id }
+    child_index = options.index { |_label, id| id == categories(:subcategory).id }
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index
+  end
+end
diff --git a/test/models/rule/condition_filter/transaction_category_test.rb b/test/models/rule/condition_filter/transaction_category_test.rb
new file mode 100644
index 000000000..9569bc050
--- /dev/null
+++ b/test/models/rule/condition_filter/transaction_category_test.rb
@@ -0,0 +1,28 @@
+require "test_helper"
+
+class Rule::ConditionFilter::TransactionCategoryTest < ActiveSupport::TestCase
+  setup do
+    @rule = rules(:one)
+    @filter = Rule::ConditionFilter::TransactionCategory.new(@rule)
+  end
+
+  test "options groups subcategories immediately after their parent" do
+    options = @filter.options
+
+    parent_index = options.index { |_label, id| id == categories(:food_and_drink).id }
+    child_index = options.index { |_label, id| id == categories(:subcategory).id }
+
+    assert_not_nil parent_index
+    assert_not_nil child_index
+    assert_equal parent_index + 1, child_index
+  end
+
+  test "options indents subcategory labels" do
+    options = @filter.options
+
+    child_label, = options.find { |_label, id| id == categories(:subcategory).id }
+
+    assert_not_equal categories(:subcategory).name, child_label
+    assert_includes child_label, categories(:subcategory).name
+  end
+end