Test if insert_all / upsert_all apply correct values

If Rails give the database multiple values that would conflict in their identifiers (be it unique indexes or primary keys), the database has to decide which ones to apply.

For `insert_all`, this will be the first one (since on conflict, the second entry will be skipped). For `upsert_all`, this is the last one (since on each duplicate, the values get updated). This commit adds two tests to verify that.

The `upsert_all` test has be skipped on PostgreSQL, as upserting with duplicate identifiers is not supported. For more details, see rails#35531.

Author: andyundso

activerecord/test/cases/insert_all_test.rb

@@ -185,6 +185,16 @@ def test_insert_all_with_skip_duplicates_and_autonumber_id_given
     end
   end
 
+  def test_insert_all_only_applies_last_value_when_given_duplicate_identifiers
+    skip unless supports_insert_on_duplicate_skip?
+
+    Book.insert_all [
+      { id: 111, name: "expected_new_name" },
+      { id: 111, name: "unexpected_new_name" }
+    ]
+    assert_equal "expected_new_name", Book.find(111).name
+  end
+
   def test_skip_duplicates_strategy_does_not_secretly_upsert
     skip unless supports_insert_on_duplicate_skip?
 
@@ -399,6 +409,18 @@ def test_upsert_all_updates_existing_record_by_primary_key
     assert_equal "New edition", Book.find(1).name
   end
 
+  def test_upsert_all_only_applies_last_value_when_given_duplicate_identifiers
+    skip unless supports_insert_on_duplicate_update? && !current_adapter?(:PostgreSQLAdapter)
+
+    Book.create!(id: 112, name: "original_name")
+
+    Book.upsert_all [
+      { id: 112, name: "unexpected_new_name" },
+      { id: 112, name: "expected_new_name" }
+    ]
+    assert_equal "expected_new_name", Book.find(112).name
+  end
+
   def test_upsert_all_does_notupdates_existing_record_by_when_there_is_no_key
     skip unless supports_insert_on_duplicate_update? && !supports_insert_conflict_target?