#create_or_find_by/!: add more tests and fix docs (#34653)

* `#create_or_find_by/!`: add more tests

* Fix docs of `create_or_find_by`

This method uses `find_by!` internally.

activerecord/lib/active_record/relation.rb

@@ -163,7 +163,7 @@ module ActiveRecord
     # Attempts to create a record with the given attributes in a table that has a unique constraint
     # on one or several of its columns. If a row already exists with one or several of these
     # unique constraints, the exception such an insertion would normally raise is caught,
-    # and the existing record with those attributes is found using #find_by.
+    # and the existing record with those attributes is found using #find_by!.
     #
     # This is similar to #find_or_create_by, but avoids the problem of stale reads between the SELECT
     # and the INSERT, as that method needs to first query the table, then attempt to insert a row
@@ -173,7 +173,7 @@ module ActiveRecord
     #
     # * The underlying table must have the relevant columns defined with unique constraints.
     # * A unique constraint violation may be triggered by only one, or at least less than all,
-    #   of the given attributes. This means that the subsequent #find_by may fail to find a
+    #   of the given attributes. This means that the subsequent #find_by! may fail to find a
     #   matching record, which will then raise an <tt>ActiveRecord::RecordNotFound</tt> exception,
     #   rather than a record with the given attributes.
     # * While we avoid the race condition between SELECT -> INSERT from #find_or_create_by,

activerecord/test/cases/relations_test.rb

@@ -1315,6 +1315,13 @@ class RelationTest < ActiveRecord::TestCase
     assert_not_equal subscriber, Subscriber.create_or_find_by(nick: "cat")
   end
 
+  def test_create_or_find_by_should_not_raise_due_to_validation_errors
+    assert_nothing_raised do
+      bird = Bird.create_or_find_by(color: "green")
+      assert_predicate bird, :invalid?
+    end
+  end
+
   def test_create_or_find_by_with_non_unique_attributes
     Subscriber.create!(nick: "bob", name: "the builder")
 
@@ -1334,6 +1341,38 @@ class RelationTest < ActiveRecord::TestCase
     end
   end
 
+  def test_create_or_find_by_with_bang
+    assert_nil Subscriber.find_by(nick: "bob")
+
+    subscriber = Subscriber.create!(nick: "bob")
+
+    assert_equal subscriber, Subscriber.create_or_find_by!(nick: "bob")
+    assert_not_equal subscriber, Subscriber.create_or_find_by!(nick: "cat")
+  end
+
+  def test_create_or_find_by_with_bang_should_raise_due_to_validation_errors
+    assert_raises(ActiveRecord::RecordInvalid) { Bird.create_or_find_by!(color: "green") }
+  end
+
+  def test_create_or_find_by_with_bang_with_non_unique_attributes
+    Subscriber.create!(nick: "bob", name: "the builder")
+
+    assert_raises(ActiveRecord::RecordNotFound) do
+      Subscriber.create_or_find_by!(nick: "bob", name: "the cat")
+    end
+  end
+
+  def test_create_or_find_by_with_bang_within_transaction
+    assert_nil Subscriber.find_by(nick: "bob")
+
+    subscriber = Subscriber.create!(nick: "bob")
+
+    Subscriber.transaction do
+      assert_equal subscriber, Subscriber.create_or_find_by!(nick: "bob")
+      assert_not_equal subscriber, Subscriber.create_or_find_by!(nick: "cat")
+    end
+  end
+
   def test_find_or_initialize_by
     assert_nil Bird.find_by(name: "bob")