diff --git a/.gitignore b/.gitignore
index eba4eea..02961fb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,6 +15,9 @@
 /config/master.key
 /config/puma.rb
 
+# Ignore test database.
+/db/test.sqlite3
+
 # Ignore all logfiles and tempfiles.
 /log/*
 /tmp/*
@@ -30,7 +33,7 @@
 
 /tmp/restart.txt
 
-# Ignore user files
+# Ignore user files.
 /.bash_history
 /.byebug_history
 /.config
@@ -38,6 +41,7 @@
 /.lesshst
 /.local
 /.mysql_history
+/.sqlite_history
 /.ssh
 /.vim
 /.viminfo
diff --git a/README.md b/README.md
index 62de50b..ee82bb7 100644
--- a/README.md
+++ b/README.md
@@ -119,9 +119,10 @@ Contributing
 
 ### Gems
 
-Apart from database adapter, install development and testing gems:
+Install development and testing gems, including at least MySQL and SQLite
+database adapters:
 
-    bundle config --local with mysql development test
+    bundle config --local with development test mysql sqlite
 
 ### Configuration
 
@@ -134,8 +135,9 @@ assets.
 
 ### Database
 
-Grant database user privileges for development and test environments,
-possibly with different Ruby versions:
+Grant database user privileges for development and test environments. Example
+below shows how to grant privileges to all databases which names start with
+`fixinme-` on MySQL:
 
     > mysql -p
     mysql> create user `fixinme-dev`@localhost identified by '<some password>';
@@ -148,6 +150,10 @@ Starting application server in development environment:
 
     bundle exec rails s -e development
 
+Accessing database console when more than one test db is present:
+
+    bundle exec rails dbconsole -e test --db sqlite3
+
 For running rake tasks, prepend command with environment:
 
     RAILS_ENV=development bundle exec rails ...
@@ -160,14 +166,22 @@ Tests need to be run from within toplevel application directory:
 
         bundle exec rails test:system
 
-* system test(s) with seed/test name specified:
+* system test(s) with seed or test name specified:
 
-        bundle exec rails test:system --seed 64690 --name test_add_unit
+        bundle exec rails test:system --include test_add_unit --seed 64690
 
-* all tests from one file, with optional seed:
+* all tests from one file, optionally with seed:
 
         bundle exec rails test test/system/users_test.rb --seed 1234
 
+* system tests for selected database configuration (if multiple present):
+
+        bundle exec rails test:system --include /^test_sqlite3_/
+
+* single system test for all database configurations (if multiple present):
+
+        bundle exec rails test:system --include /^test_\\w+_add_unit$/
+
 ### Icons
 
 Pictogrammers Material Design Icons: https://pictogrammers.com/library/mdi/
diff --git a/config/database.yml.dist b/config/database.yml.dist
index 5d079fe..25c80c4 100644
--- a/config/database.yml.dist
+++ b/config/database.yml.dist
@@ -24,27 +24,45 @@
 # Read https://guides.rubyonrails.org/configuring.html#configuring-a-database
 # for a full overview on how database connection configuration can be specified.
 default: &default
-  adapter: mysql2
-  encoding: utf8mb4
-  collation: utf8mb4_0900_as_ci
-  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
-  username: fixinme
-  password: Some-password1%
-  socket: /run/mysqld/mysqld.sock
+  pool: <%= ENV.fetch('RAILS_MAX_THREADS', 3) %>
+
+#mysql_default: &mysql_default
+#  <<: *default
+#  username: fixinme
+#  password: Some-password1%
+#  host: 127.0.0.1
+#  encoding: utf8mb4
+#  collation: utf8mb4_0900_as_ci
 
 production:
   <<: *default
-  database: fixinme
+  adapter: sqlite3
+  database: db/production.sqlite3
 
-# Unless you're planning on developing the application, you can skip
+# Unless you're planning on developing the application, you can skip/remove
 # configurations for development and test databases altogether.
 #development:
-#  <<: *default
+#  <<: *mysql_default
+#  adapter: mysql2
 #  database: fixinme_dev
 
-# Warning: The database defined as "test" will be erased and
+# Warning: The database(s) defined as "test" will be erased and
 # re-generated from your development database when you run "rake".
 # Do not set this db to the same as development or production.
 #test:
-#  <<: *default
+#  <<: *mysql_default
+#  adapter: mysql2
 #  database: fixinme_test
+
+# Multiple test databases can be provided. When more than one test db is
+# present, every test task (test, test:models, test:system, etc.) runs against
+# all of them.
+#test:
+#  mysql2:
+#    <<: *mysql_default
+#    adapter: mysql2
+#    database: fixinme_test
+#  sqlite3:
+#    <<: *default
+#    adapter: sqlite3
+#    database: db/test.sqlite3
diff --git a/db/schema.rb b/db/schema.rb
index 3205384..9d97716 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2025_01_21_230456) do
+ActiveRecord::Schema[8.0].define(version: 2025_01_21_230456) do
   create_table "quantities", charset: "utf8mb4", collation: "utf8mb4_0900_as_ci", force: :cascade do |t|
     t.bigint "user_id"
     t.string "name", limit: 31, null: false
diff --git a/db/sqlite3_schema.rb b/db/sqlite3_schema.rb
new file mode 100644
index 0000000..5002cdb
--- /dev/null
+++ b/db/sqlite3_schema.rb
@@ -0,0 +1,80 @@
+# This file is auto-generated from the current state of the database. Instead
+# of editing this file, please use the migrations feature of Active Record to
+# incrementally modify your database, and then regenerate this schema definition.
+#
+# This file is the source Rails uses to define your schema when running `bin/rails
+# db:schema:load`. When creating a new database, `bin/rails db:schema:load` tends to
+# be faster and is potentially less error prone than running all of your
+# migrations from scratch. Old migrations may fail to apply correctly if those
+# migrations use external dependencies or application code.
+#
+# It's strongly recommended that you check this file into your version control system.
+
+ActiveRecord::Schema[8.0].define(version: 2025_01_21_230456) do
+  create_table "quantities", force: :cascade do |t|
+    t.integer "user_id"
+    t.string "name", limit: 31, null: false
+    t.text "description"
+    t.integer "parent_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.integer "depth", default: 0, null: false
+    t.string "pathname", limit: 511, null: false
+    t.index ["parent_id"], name: "index_quantities_on_parent_id"
+    t.index ["user_id", "parent_id", "name"], name: "index_quantities_on_user_id_and_parent_id_and_name", unique: true
+    t.index ["user_id"], name: "index_quantities_on_user_id"
+  end
+
+  create_table "readouts", force: :cascade do |t|
+    t.integer "user_id", null: false
+    t.integer "quantity_id", null: false
+    t.integer "category", default: 0, null: false
+    t.float "value", limit: 53, null: false
+    t.integer "unit_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["quantity_id", "created_at"], name: "index_readouts_on_quantity_id_and_created_at", unique: true
+    t.index ["quantity_id"], name: "index_readouts_on_quantity_id"
+    t.index ["unit_id"], name: "index_readouts_on_unit_id"
+    t.index ["user_id"], name: "index_readouts_on_user_id"
+  end
+
+  create_table "units", force: :cascade do |t|
+    t.integer "user_id"
+    t.string "symbol", limit: 15, null: false
+    t.text "description"
+    t.decimal "multiplier", precision: 30, scale: 15, default: "1.0", null: false
+    t.integer "base_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["base_id"], name: "index_units_on_base_id"
+    t.index ["user_id", "symbol"], name: "index_units_on_user_id_and_symbol", unique: true
+    t.index ["user_id"], name: "index_units_on_user_id"
+  end
+
+  create_table "users", force: :cascade do |t|
+    t.string "email", limit: 64, null: false
+    t.integer "status", default: 0, null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.string "encrypted_password", default: "", null: false
+    t.string "reset_password_token"
+    t.datetime "reset_password_sent_at"
+    t.datetime "remember_created_at"
+    t.string "confirmation_token"
+    t.datetime "confirmed_at"
+    t.datetime "confirmation_sent_at"
+    t.string "unconfirmed_email", limit: 64
+    t.index ["confirmation_token"], name: "index_users_on_confirmation_token", unique: true
+    t.index ["email"], name: "index_users_on_email", unique: true
+    t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
+  end
+
+  add_foreign_key "quantities", "quantities", column: "parent_id", on_delete: :cascade
+  add_foreign_key "quantities", "users"
+  add_foreign_key "readouts", "quantities"
+  add_foreign_key "readouts", "units"
+  add_foreign_key "readouts", "users"
+  add_foreign_key "units", "units", column: "base_id", on_delete: :cascade
+  add_foreign_key "units", "users"
+end
diff --git a/test/application_system_test_case.rb b/test/application_system_test_case.rb
index 4ba8106..e03481f 100644
--- a/test/application_system_test_case.rb
+++ b/test/application_system_test_case.rb
@@ -39,6 +39,32 @@ class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
   end
   alias :t :translate
 
+  DB_CONFIGS = ActiveRecord::Base.configurations.configs_for(env_name: "test")
+  TEST_CONFIGS = Hash.new(DB_CONFIGS.first.name.to_sym)
+  class << self
+    # NOTE: alternative to current solution is to create shards:
+    #   ActiveRecord::Base.connects_to(
+    #     shards: {mysql2: {writing: :mysql2}, sqlite3: {writing: :sqlite3}}
+    #   )
+    # and use them in one of the following ways:
+    # * set config.active_record.shard_selector/shard_resolver
+    # * run tests within: ActiveRecord::Base.connected_to(shard: :sqlite3) { test_ }
+    # Remove this note once current solution is confirmed to work.
+    #
+    # Test block should not be modified here, as it would change its binding from
+    # instance level to class level.
+    if DB_CONFIGS.many?
+      def test(name, ...)
+        DB_CONFIGS.each do |config|
+          TEST_CONFIGS[super("#{config.name} #{name}", ...)] = config.name.to_sym
+        end
+      end
+    end
+  end
+  setup do
+    ActiveRecord::Base.establish_connection(TEST_CONFIGS[name.to_sym])
+  end
+
   #def assert_stale(element)
   #  assert_raises(Selenium::WebDriver::Error::StaleElementReferenceError) { element.tag_name }
   #end
diff --git a/test/controllers/users_controller_test.rb b/test/controllers/users_controller_test.rb
index bda70d8..9097514 100644
--- a/test/controllers/users_controller_test.rb
+++ b/test/controllers/users_controller_test.rb
@@ -1,5 +1,7 @@
 require "test_helper"
 
+# TODO: make sure tested actions are covered by system tests and remove all
+# controller tests.
 class UsersControllerTest < ActionDispatch::IntegrationTest
   setup do
     @user = users(:one)
diff --git a/test/models/user_test.rb b/test/models/user_test.rb
index 5c07f49..5a2150d 100644
--- a/test/models/user_test.rb
+++ b/test/models/user_test.rb
@@ -1,5 +1,6 @@
 require "test_helper"
 
+# TODO: remove model tests
 class UserTest < ActiveSupport::TestCase
   # test "the truth" do
   #   assert true
diff --git a/test/system/users_test.rb b/test/system/users_test.rb
index b012bf4..5654a56 100644
--- a/test/system/users_test.rb
+++ b/test/system/users_test.rb
@@ -204,6 +204,7 @@ class UsersTest < ApplicationSystemTestCase
 
   test 'update profile' do
     # TODO
+    assert true
   end
 
   test 'update status' do