old_contents: def test_eval_expr1(eval_expr):
      assert 2 == eval_expr('1 + 1')
  
  def test_eval_expr2(eval_expr):
      assert 0 == eval_expr('1 - 1')
  
  
  def test_eval_expr3(eval_expr):
      assert True == eval_expr('true')
  
  def test_eval_expr4(eval_expr):
      assert True == eval_expr('true == true')
  
  def test_eval_expr5(eval_expr):
      assert False == eval_expr('true ~= true')
  
  def test_eval_expr6(eval_expr):
      assert False == eval_expr('not true')
  
new_contents: def test_eval_nums1(eval_expr):
      assert 2 == eval_expr('1 + 1')
  
  def test_eval_nums2(eval_expr):
      assert 0 == eval_expr('1 - 1')
  
  def test_eval_nums3(eval_expr):
      assert 0 == eval_expr('-1 + 1')
  
  def test_eval_nums4(eval_expr):
      assert 7 == eval_expr('1 + 2 * 3')
  
  def test_eval_nums5(eval_expr):
      assert 5 == eval_expr('1 * 2 + 3')
  
  
  def test_eval_expr3(eval_expr):
      assert True == eval_expr('true')
  
  def test_eval_expr4(eval_expr):
      assert True == eval_expr('true == true')
  
  def test_eval_expr5(eval_expr):
      assert False == eval_expr('true ~= true')
  
  def test_eval_expr6(eval_expr):
      assert False == eval_expr('not true')
  
subject: add num tests