diff --git a/test/mkmf/test_libs.rb b/test/mkmf/test_libs.rb
new file mode 100644
index 0000000000..67722afa67
--- /dev/null
+++ b/test/mkmf/test_libs.rb
@@ -0,0 +1,69 @@
+require_relative 'base'
+
+class TestMkmf
+  class TestLibs < TestMkmf
+    def test_split_libs
+      assert_equal(%w[-lfoo -lbar], split_libs("-lfoo -lbar"))
+      assert_equal(%w[-ObjC -framework\ Ruby], split_libs("-ObjC -framework Ruby"), 'Bug #6987')
+    end
+
+    def assert_in_order(array, x, y, mesg = nil)
+      mesg = "#{x} must proceed to #{y}#{': ' if mesg}#{mesg}"
+      assert_operator(array.index(x), :<, array.rindex(y), mesg)
+    end
+
+    def test_merge_simple
+      bug = '[ruby-dev:21765]'
+      assert_equal([], merge_libs(%w[]))
+      assert_equal(%w[a b], merge_libs(%w[a], %w[b]))
+      array = merge_libs(%w[a c], %w[b])
+      assert_in_order(array, "a", "c", bug)
+    end
+
+    def test_merge_seq
+      bug = '[ruby-dev:21765]'
+      array = merge_libs(%w[a c d], %w[c b e])
+      assert_in_order(array, "a", "c", bug)
+      assert_in_order(array, "c", "d", bug)
+      assert_in_order(array, "c", "b", bug)
+      assert_in_order(array, "b", "e", bug)
+    end
+
+    def test_merge_seq_pre
+      bug = '[ruby-dev:21765]'
+      array = merge_libs(%w[a c d], %w[b c d e])
+      assert_in_order(array, "a", "c", bug)
+      assert_in_order(array, "c", "d", bug)
+      assert_in_order(array, "b", "c", bug)
+      assert_in_order(array, "d", "e", bug)
+    end
+
+    def test_merge_cyclic
+      bug = '[ruby-dev:21765]'
+      array = merge_libs(%w[a c d], %w[b c b])
+      assert_in_order(array, "a", "c", bug)
+      assert_in_order(array, "c", "d", bug)
+      assert_in_order(array, "b", "c", bug)
+      assert_in_order(array, "c", "b", bug)
+    end
+
+    def test_merge_cyclic_2
+      bug = '[ruby-dev:21765]'
+      array = merge_libs(%w[a c a d], %w[b c b])
+      assert_in_order(array, "a", "c", bug)
+      assert_in_order(array, "c", "a", bug)
+      assert_in_order(array, "c", "d", bug)
+      assert_in_order(array, "a", "d", bug)
+      assert_in_order(array, "b", "c", bug)
+      assert_in_order(array, "c", "b", bug)
+    end
+
+    def test_merge_reversal
+      bug = '[ruby-dev:22440]'
+      array = merge_libs(%w[a b c], %w[c d a])
+      assert_in_order(array, "a", "b" , bug)
+      assert_in_order(array, "c", "d" , bug)
+      ## assume that a and c have no dependency
+    end
+  end
+end if RUBY_ENGINE == "ruby"