ActiveRecord::Base is not `connected?` after successful `establish_connection`

_rails#32918.rb

# frozen_string_literal: true

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

a = gemfile(true) do
  source "https://rubygems.org"

  gem "activerecord", "5.2.0"
  gem "sqlite3", "1.3.13"
  gem "rake", "~> 10.0"
  gem "rspec", "~> 3.0"
end

require "active_record"
require "rspec"

sqlite3_config = {
  "development" => {
    "adapter" => "sqlite3",
    "database" => "development.sqlite3"
  }
}

RSpec.configure do |config|
  config.formatter = "documentation"
end

RSpec.describe "connecting", :aggregate_failures do
  it "is not connected by default" do
    expect(ActiveRecord::Base.connected?).to be_falsey
    expect{ ActiveRecord::Base.connection }.to raise_error(ActiveRecord::ConnectionNotEstablished)
    expect{ ActiveRecord::Base.retrieve_connection }.to raise_error(ActiveRecord::ConnectionNotEstablished)
  end

  context "connected" do
    before do
      ActiveRecord::Base.establish_connection(sqlite3_config["development"])
      # Issue closed, fix is to add `ActiveRecord::Base.connection` here
    end

    after do
      ActiveRecord::Base.remove_connection
    end

    it "is connected" do
      expect(ActiveRecord::Base.connected?).to be_truthy
      expect(ActiveRecord::Base.connection).to be_kind_of(ActiveRecord::ConnectionAdapters::SQLite3Adapter)
      expect(ActiveRecord::Base.retrieve_connection).to eq(ActiveRecord::Base.connection)
    end
  end
end

output.txt

$ rspec _rails#32918.rb
Fetching gem metadata from https://rubygems.org/........
Resolving dependencies...
Using rake 10.5.0
Using concurrent-ruby 1.0.5
Using i18n 1.0.1
Using minitest 5.11.3
Using thread_safe 0.3.6
Using tzinfo 1.2.5
Using activesupport 5.2.0
Using activemodel 5.2.0
Using arel 9.0.0
Using activerecord 5.2.0
Using bundler 1.16.0
Using diff-lcs 1.3
Using rspec-support 3.7.1
Using rspec-core 3.7.1
Using rspec-expectations 3.7.0
Using rspec-mocks 3.7.0
Using rspec 3.7.0
Using sqlite3 1.3.13

connecting
  is not connected by default
  connected
    is connected (FAILED - 1)

Failures:

  1) connecting connected is connected
     Failure/Error: expect(ActiveRecord::Base.connected?).to be_truthy

       expected: truthy value
            got: false
     # ./test.rb:50:in `block (3 levels) in <top (required)>'

Finished in 0.23324 seconds (files took 2.78 seconds to load)
2 examples, 1 failure

Failed examples:

rspec ./test.rb:49 # connecting connected is connected