Seperate unit and integration tests.

This makes it easier to re-use the integration tests in a seperate gem that
optimizes parts of liquid with a native implementation.

test/unit/strainer_unit_test.rb

@@ -0,0 +1,70 @@
+require 'test_helper'
+
+class StrainerUnitTest < Test::Unit::TestCase
+  include Liquid
+
+  module AccessScopeFilters
+    def public_filter
+      "public"
+    end
+
+    def private_filter
+      "private"
+    end
+    private :private_filter
+  end
+
+  Strainer.global_filter(AccessScopeFilters)
+
+  def test_strainer
+    strainer = Strainer.create(nil)
+    assert_equal 5, strainer.invoke('size', 'input')
+    assert_equal "public", strainer.invoke("public_filter")
+  end
+
+  def test_stainer_raises_argument_error
+    strainer = Strainer.create(nil)
+    assert_raises(Liquid::ArgumentError) do
+      strainer.invoke("public_filter", 1)
+    end
+  end
+
+  def test_strainer_only_invokes_public_filter_methods
+    strainer = Strainer.create(nil)
+    assert_equal false, strainer.invokable?('__test__')
+    assert_equal false, strainer.invokable?('test')
+    assert_equal false, strainer.invokable?('instance_eval')
+    assert_equal false, strainer.invokable?('__send__')
+    assert_equal true, strainer.invokable?('size') # from the standard lib
+  end
+
+  def test_strainer_returns_nil_if_no_filter_method_found
+    strainer = Strainer.create(nil)
+    assert_nil strainer.invoke("private_filter")
+    assert_nil strainer.invoke("undef_the_filter")
+  end
+
+  def test_strainer_returns_first_argument_if_no_method_and_arguments_given
+    strainer = Strainer.create(nil)
+    assert_equal "password", strainer.invoke("undef_the_method", "password")
+  end
+
+  def test_strainer_only_allows_methods_defined_in_filters
+    strainer = Strainer.create(nil)
+    assert_equal "1 + 1", strainer.invoke("instance_eval", "1 + 1")
+    assert_equal "puts",  strainer.invoke("__send__", "puts", "Hi Mom")
+    assert_equal "has_method?", strainer.invoke("invoke", "has_method?", "invoke")
+  end
+
+  def test_strainer_uses_a_class_cache_to_avoid_method_cache_invalidation
+    a, b = Module.new, Module.new
+    strainer = Strainer.create(nil, [a,b])
+    assert_kind_of Strainer, strainer
+    assert_kind_of a, strainer
+    assert_kind_of b, strainer
+    Strainer.class_variable_get(:@@filters).each do |m|
+      assert_kind_of m, strainer
+    end
+  end
+
+end # StrainerTest