The exhaustive tests are in test/controller/html/sanitizer_test.rb. This tests the that the helpers hook up correctly to the sanitizer classes.

Methods
A
T
Included Modules
Instance Public methods
assert_sanitized(text, expected = nil)
# File actionpack/test/template/sanitize_helper_test.rb, line 54
def assert_sanitized(text, expected = nil)
  assert_equal((expected || text), sanitize(text))
end
test_sanitize_form()
# File actionpack/test/template/sanitize_helper_test.rb, line 21
def test_sanitize_form
  assert_sanitized "<form action=\"/foo/bar\" method=\"post\"><input></form>", ''
end
test_sanitize_is_marked_safe()
# File actionpack/test/template/sanitize_helper_test.rb, line 50
def test_sanitize_is_marked_safe
  assert sanitize("<html><script></script></html>").html_safe?
end
test_should_sanitize_illegal_style_properties()
# File actionpack/test/template/sanitize_helper_test.rb, line 25
def test_should_sanitize_illegal_style_properties
  raw      = %Q(display:block; position:absolute; left:0; top:0; width:100%; height:100%; z-index:1; background-color:black; background-image:url(http://www.ragingplatypus.com/i/cam-full.jpg); background-x:center; background-y:center; background-repeat:repeat;)
  expected = %Q(display: block; width: 100%; height: 100%; background-color: black; background-image: ; background-x: center; background-y: center;)
  assert_equal expected, sanitize_css(raw)
end
test_strip_tags()
# File actionpack/test/template/sanitize_helper_test.rb, line 31
def test_strip_tags
  assert_equal("<<<bad html", strip_tags("<<<bad html"))
  assert_equal("<<", strip_tags("<<<bad html>"))
  assert_equal("Dont touch me", strip_tags("Dont touch me"))
  assert_equal("This is a test.", strip_tags("<p>This <u>is<u> a <a href='test.html'><strong>test</strong></a>.</p>"))
  assert_equal("Weirdos", strip_tags("Wei<<a>a onclick='alert(document.cookie);'</a>/>rdos"))
  assert_equal("This is a test.", strip_tags("This is a test."))
  assert_equal(
  %Q{This is a test.\n\n\nIt no longer contains any HTML.\n}, strip_tags(
  %Q{<title>This is <b>a <a href="" target="_blank">test</a></b>.</title>\n\n<!-- it has a comment -->\n\n<p>It no <b>longer <strong>contains <em>any <strike>HTML</strike></em>.</strong></b></p>\n}))
  assert_equal "This has a  here.", strip_tags("This has a <!-- comment --> here.")
  [nil, '', '   '].each do |blank|
    stripped = strip_tags(blank)
    assert_equal blank, stripped
  end
  assert_equal "", strip_tags("<script>")
  assert_equal "something &lt;img onerror=alert(1337)", ERB::Util.html_escape(strip_tags("something <img onerror=alert(1337)"))
end