Tty: Avoid truncating if not sensible

This causes truncate to simply return the original string if the
terminal is not very wide, or if the terminal is unsupported.

Library/Homebrew/test/test_utils.rb

@@ -9,9 +9,13 @@ class TtyTests < Homebrew::TestCase
   end
 
   def test_truncate
-    Tty.stubs(:width).returns 10
+    Tty.stubs(:width).returns 15
-    assert_equal "foobar", Tty.truncate("foobar something very long")
+    assert_equal "foobar some", Tty.truncate("foobar something very long")
-    assert_equal "trunca", Tty.truncate("truncate")
+    assert_equal "truncate", Tty.truncate("truncate")
+
+    # When the terminal is unsupported, we report 0 width
+    Tty.stubs(:width).returns 0
+    assert_equal "foobar something very long", Tty.truncate("foobar something very long")
   end
 
   def test_no_tty_formatting

Library/Homebrew/utils.rb

@@ -65,7 +65,8 @@ class Tty
     end
 
     def truncate(str)
-      str.to_s[0, width - 4]
+      w = width
+      w > 10 ? str.to_s[0, w - 4] : str
     end
 
     private