Add additional test for :single_encoding

Author: wishdev

test/csv/test_table.rb

@@ -381,6 +381,16 @@ def test_to_csv_single_encoding
     assert_equal('ASCII-8BIT', table.to_csv(single_encoding: true).encoding.to_s)
     assert_equal('UTF-8', table.to_csv(encoding: 'UTF-8').encoding.to_s)
     assert_raises(Encoding::CompatibilityError) {table.to_csv}
+
+    headers = %w{id language description}
+    rows = [ CSV::Row.new(headers, ["English", "ascii-only row"]),
+             CSV::Row.new(headers, ["Français", "alphabet + cédille first non-ascii row"]),
+             CSV::Row.new(headers, ["Español", "alphabet + ntilde character row"])]
+    table = CSV::Table.new(rows)
+
+    assert_equal('UTF-8', table.to_csv.encoding.to_s)
+    assert_equal('UTF-8', table.to_csv(single_encoding: true).encoding.to_s)
+    assert_equal(table.to_csv, table.to_csv(single_encoding: true))
   end
 
   def test_append