ahem/spec/ast/assignment_spec.rb

RSpec.describe AST::Assignment do
  it 'reassigns an existing variable' do
    env = Environment.new
    AST::VariableDeclaration.new(
      AST::Identifier.new('x'),
      AST::Number.new(5.0),
    ).execute(env)
    AST::Assignment.new(
      AST::Identifier.new('x'),
      AST::Number.new(6.0),
    ).execute(env)
    expect(env.get('x').execute(env)).to eq(6.0)
  end

  it 'raises for an undeclared variable' do
    env = Environment.new
    expect {
      AST::Assignment.new(
        AST::Identifier.new('x'),
        AST::Number.new(6.0),
      ).execute(env)
    }.to raise_error("Undefined variable x")

  end
end