Worksheet name uniqueness doesn't apply to itself

This constraint would prevent you from creating a new worksheet
with the name that it would have gotten by default.

lib/axlsx/workbook/worksheet/worksheet.rb

@@ -637,14 +637,14 @@ def outline(collection, range, level = 1, collapsed = true)
  end
  sheet_view.show_outline_symbols = true
  end
-
  end
+
  def validate_sheet_name(name)
  DataTypeValidator.validate "Worksheet.name", String, name
  raise ArgumentError, (ERR_SHEET_NAME_TOO_LONG % name) if name.size > 31
  raise ArgumentError, (ERR_SHEET_NAME_CHARACTER_FORBIDDEN % name) if '[]*/\?:'.chars.any? { |char| name.include? char }
  name = Axlsx::coder.encode(name)
- sheet_names = @workbook.worksheets.map { |s| s.name }
+ sheet_names = @workbook.worksheets.reject { |s| s == self }.map { |s| s.name }
  raise ArgumentError, (ERR_DUPLICATE_SHEET_NAME % name) if sheet_names.include?(name)
  end
 

test/workbook/worksheet/tc_worksheet.rb

@@ -405,6 +405,11 @@ def test_name_unique
  assert_raise(ArgumentError, "worksheet name must be unique") { n = @ws.name; @ws.workbook.add_worksheet(:name=> n) }
  end
 
+ def test_name_unique_only_checks_other_worksheet_names
+ assert_nothing_raised { @ws.name = @ws.name }
+ assert_nothing_raised { Axlsx::Package.new.workbook.add_worksheet :name => 'Sheet1' }
+ end
+
  def test_name_size
  assert_raise(ArgumentError, "name too long!") { @ws.name = Array.new(32, "A").join() }
  assert_nothing_raised { @ws.name = Array.new(31, "A").join() }