diff --git a/test/controllers/controller_test.rb b/test/controllers/controller_test.rb
index e2568f97..d27eb2e6 100644
--- a/test/controllers/controller_test.rb
+++ b/test/controllers/controller_test.rb
@@ -494,15 +494,15 @@ def test_sorting_by_relationship_field
 
     assert_response :success
     assert json_response['data'].length > 10, 'there are enough records to show sort'
+    expected = Post
+      .all
+      .left_joins(:author)
+      .merge(Person.order(name: :asc))
+      .map(&:id)
+      .map(&:to_s)
+    ids = json_response['data'].map {|data| data['id'] }
 
-    # Postgres sorts nulls last, whereas sqlite and mysql sort nulls first
-    if ENV['DATABASE_URL'].starts_with?('postgres')
-      assert_equal '17', json_response['data'][-1]['id'], 'nil is at the start'
-      assert_equal post.id.to_s, json_response['data'][0]['id'], 'alphabetically first user is not first'
-    else
-      assert_equal '17', json_response['data'][0]['id'], 'nil is at the end'
-      assert_equal post.id.to_s, json_response['data'][1]['id'], 'alphabetically first user is second'
-    end
+    assert_equal expected, ids, "since adapter_sorts_nulls_last=#{adapter_sorts_nulls_last}"
   end
 
   def test_desc_sorting_by_relationship_field
@@ -512,14 +512,15 @@ def test_desc_sorting_by_relationship_field
     assert_response :success
     assert json_response['data'].length > 10, 'there are enough records to show sort'
 
-    # Postgres sorts nulls last, whereas sqlite and mysql sort nulls first
-    if ENV['DATABASE_URL'].starts_with?('postgres')
-      assert_equal '17', json_response['data'][0]['id'], 'nil is at the start'
-      assert_equal post.id.to_s, json_response['data'][-1]['id']
-    else
-      assert_equal '17', json_response['data'][-1]['id'], 'nil is at the end'
-      assert_equal post.id.to_s, json_response['data'][-2]['id'], 'alphabetically first user is second last'
-    end
+    expected = Post
+      .all
+      .left_joins(:author)
+      .merge(Person.order(name: :desc))
+      .map(&:id)
+      .map(&:to_s)
+    ids = json_response['data'].map {|data| data['id'] }
+
+    assert_equal expected, ids, "since adapter_sorts_nulls_last=#{adapter_sorts_nulls_last}"
   end
 
   def test_sorting_by_relationship_field_include
@@ -529,13 +530,15 @@ def test_sorting_by_relationship_field_include
     assert_response :success
     assert json_response['data'].length > 10, 'there are enough records to show sort'
 
-    if ENV['DATABASE_URL'].starts_with?('postgres')
-      assert_equal '17', json_response['data'][-1]['id'], 'nil is at the top'
-      assert_equal post.id.to_s, json_response['data'][0]['id']
-    else
-      assert_equal '17', json_response['data'][0]['id'], 'nil is at the top'
-      assert_equal post.id.to_s, json_response['data'][1]['id'], 'alphabetically first user is second'
-    end
+    expected = Post
+      .all
+      .left_joins(:author)
+      .merge(Person.order(name: :asc))
+      .map(&:id)
+      .map(&:to_s)
+    ids = json_response['data'].map {|data| data['id'] }
+
+    assert_equal expected, ids, "since adapter_sorts_nulls_last=#{adapter_sorts_nulls_last}"
   end
 
   def test_invalid_sort_param
@@ -4772,11 +4775,11 @@ def test_fetch_robots_with_sort_by_name
     assert_cacheable_get :index, params: {sort: 'name'}
     assert_response :success
 
-    if ENV['DATABASE_URL'].starts_with?('postgres')
-      assert_equal 'jane', json_response['data'].first['attributes']['name']
-    else
-      assert_equal 'John', json_response['data'].first['attributes']['name']
-    end
+    expected_names = Robot
+      .all
+      .order(name: :asc)
+      .map(&:name)
+    assert_equal expected_names.first, json_response['data'].first['attributes']['name'], "since adapter_sorts_nulls_last=#{adapter_sorts_nulls_last}"
   end
 
   def test_fetch_robots_with_sort_by_lower_name
diff --git a/test/integration/requests/request_test.rb b/test/integration/requests/request_test.rb
index 1863b5c7..f66e80af 100644
--- a/test/integration/requests/request_test.rb
+++ b/test/integration/requests/request_test.rb
@@ -1443,16 +1443,32 @@ def test_sort_primary_attribute
   end
 
   def test_sort_included_attribute
-    # Postgres sorts nulls last, whereas sqlite and mysql sort nulls first
-    pg = ENV['DATABASE_URL'].starts_with?('postgres')
-
     get '/api/v6/authors?sort=author_detail.author_stuff', headers: { 'Accept' => JSONAPI::MEDIA_TYPE }
     assert_jsonapi_response 200
-    assert_equal pg ? '1001' : '1000', json_response['data'][0]['id']
+    up_expected_ids = AuthorResource
+      ._model_class
+      .all
+      .left_joins(:author_detail)
+      .merge(AuthorDetail.order(author_stuff: :asc))
+      .map(&:id)
+    expected = up_expected_ids.first.to_s
+    ids = json_response['data'].map {|data| data['id'] }
+    actual = ids.first
+    assert_equal expected, actual, "since adapter_sorts_nulls_last=#{adapter_sorts_nulls_last} ands actual=#{ids} vs. expected=#{up_expected_ids}"
 
     get '/api/v6/authors?sort=-author_detail.author_stuff', headers: { 'Accept' => JSONAPI::MEDIA_TYPE }
     assert_jsonapi_response 200
-    assert_equal pg ? '1000' : '1002', json_response['data'][0]['id']
+    down_expected_ids = AuthorResource
+      ._model_class
+      .all
+      .left_joins(:author_detail)
+      .merge(AuthorDetail.order(author_stuff: :desc))
+      .map(&:id)
+    expected = down_expected_ids.first.to_s
+    ids = json_response['data'].map {|data| data['id'] }
+    actual = ids.first
+    assert_equal expected, actual, "since adapter_sorts_nulls_last=#{adapter_sorts_nulls_last} ands actual=#{ids} vs. expected=#{down_expected_ids}"
+    refute_equal up_expected_ids, down_expected_ids # sanity check
   end
 
   def test_include_parameter_quoted
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 9850a49c..91b20114 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -459,6 +459,24 @@ def run_in_transaction?
 
   self.fixture_path = "#{Rails.root}/fixtures"
   fixtures :all
+
+  def adapter_name
+    ActiveRecord::Base.connection.adapter_name
+  end
+
+  # Postgres sorts nulls last, whereas sqlite and mysql sort nulls first
+  def adapter_sorts_nulls_last
+    case adapter_name
+    when 'PostgreSQL' then true
+    when 'SQLite', 'Mysql2' then false
+    else
+      fail ArgumentError, "Unhandled adapter #{adapter_name} in #{__callee__}"
+    end
+  end
+
+  def db_true
+    ActiveRecord::Base.connection.quote(true)
+  end
 end
 
 class ActiveSupport::TestCase