```ruby
require 'testing_env'
require 'checksum'

class ChecksumTests < Homebrew::TestCase
  def test_empty?
    assert_empty Checksum.new(:sha1, '')
  end

  def test_equality
    a = Checksum.new(:sha1, 'deadbeef'*5)
    b = Checksum.new(:sha1, 'deadbeef'*5)
    assert_equal a, b

    a = Checksum.new(:sha1, 'deadbeef'*5)
    b = Checksum.new(:sha1, 'feedface'*5)
    refute_equal a, b

    a = Checksum.new(:sha1, 'deadbeef'*5)
    b = Checksum.new(:sha256, 'deadbeef'*5)
    refute_equal a, b
  end
end

```

Use TEST_SHA1 constant in checksum tests
user
```ruby
require 'testing_env'
require 'checksum'

class ChecksumTests < Homebrew::TestCase
  def test_empty?
    assert_empty Checksum.new(:sha1, '')
  end

  def test_equality
    a = Checksum.new(:sha1, TEST_SHA1)
    b = Checksum.new(:sha1, TEST_SHA1)
    assert_equal a, b

    a = Checksum.new(:sha1, TEST_SHA1)
    b = Checksum.new(:sha1, TEST_SHA1.reverse)
    refute_equal a, b

    a = Checksum.new(:sha1, TEST_SHA1)
    b = Checksum.new(:sha256, TEST_SHA256)
    refute_equal a, b
  end
end

```
assistant