class RSpec::Expectations::Configuration

Historically, the default was `false`, but `true` is recommended.
or `be_truthy` / `be_falsey` (not strict).
Configures RSpec to check predicate matchers to `be(true)` / `be(false)` (strict),

def strict_predicate_matchers=(flag)
  raise ArgumentError, "Pass `true` or `false`" unless flag == true || flag == false
  @strict_predicate_matchers = flag
end