Produce a NestedHstore hash with Rails fixtures - ruby-on-rails

Question

I have a field called custom that is defined as a NestedHstore:
# project.rb
serialize :custom, ActiveRecord::Coders::NestedHstore
I create fixtures for this model for testing:
one:
company: one
user: one
custom:
:name:
:prompt: 'What is your name?'
When this is run, the nested hashes are saved as strings, i.e. #project.custom = {"name"=>"{:prompt=>\"What is your name?\"}"}
I've gotten around this in unit and functional tests by adding a prepare_custom method that manually reconstructs the nested hash from the string BEFORE anything runs.
def prepare_custom(p)
if p.custom.present?
if p.custom.is_a? Hash
p.custom.each do |k,v|
if (v.class == String) && (v[0] == "{") && (v[-1] == "}")
p.custom[k] = eval(v)
end
end
end
p.save
p.reload
puts "*** project: #{p.inspect}"
end
end
When I run integration tests (with Capybara/Poltergeist/Puma), this happens:
prepare_custom(#project) seems to work. p.inspect at the end shows that custom is a properly nested hash.
The integration test code that runs immediately after prepare_custom seems to completely ignore that the project has been changed. It thinks p.custom[:name] is a string again.
How can I either get fixtures to save the nested hash properly, or get my integration tests to reflect the work done in prepare_custom?
Follow-up
After trying: custom: <%= {name: { prompt: 'What is your name?'}}.to_yaml.inspect %> in the fixture, we get:
ActiveRecord::StatementInvalid: ActiveRecord::StatementInvalid: PG::InternalError: ERROR: Syntax error near ':' at position 4
LINE 1: ...company_id") VALUES ('Simple prompt', 0, '---
^
: INSERT INTO "projects" ("name", "custom", "created_at", "updated_at", "id", "company_id") VALUES ('Simple prompt', '---
:name:
:prompt: What is your name?
', '2017-05-17 21:15:25', '2017-05-17 21:15:25', 159160234, 980190962, 159160234)