tweak String#undent so that only leading whitespace up to the first indentation level is gsubbed, change test_undent to reflect change and add test_undent_nested to test new behavior

Library/Homebrew/extend/string.rb

@@ -1,6 +1,6 @@
 class String
   def undent
-    gsub(/^.{#{(slice(/^ +/) || '').length}}/, "")
+    gsub(/^[ \t]{#{(slice(/^[ \t]+/) || '').length}}/, "")
   end
 
   # eg:

Library/Homebrew/test/test_string.rb

@@ -8,7 +8,7 @@ class StringTest < Homebrew::TestCase
 ....my friend over
     there
     EOS
-    assert_equal "hi\nmy friend over\nthere\n", undented
+    assert_equal "hi\n....my friend over\nthere\n", undented
   end
 
   def test_undent_not_indented
@@ -18,4 +18,17 @@ I'm not indented
     EOS
     assert_equal "hi\nI'm not indented\n", undented
   end
+
+  def test_undent_nested
+    nest = <<-EOS.undent
+      goodbye
+    EOS
+
+    undented = <<-EOS.undent
+      hello
+      #{nest}
+    EOS
+
+    assert_equal "hello\ngoodbye\n\n", undented
+  end
 end