[ruby/fiddle] Add `sym_defined?` methods to test if a symbol is defined (https://github.com/ruby/fiddle/pull/108)

I would like to check if a symbol is defined before trying to access it.
Some symbols aren't available on all platforms, so instead of raising an
exception, I want to check if it's defined first.

Today we have to do:

```ruby
begin
  addr = Fiddle::Handle.sym("something")
  # do something
rescue Fiddle::DLError
end
```

I want to write this:

```ruby
if Fiddle::Handle.sym_defined?("something")
  addr = Fiddle::Handle.sym("something")
  # do something
end
```

https://github.com/ruby/fiddle/commit/9d3371de13

Co-authored-by: Sutou Kouhei <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/test/fiddle/test_handle.rb b/test/fiddle/test_handle.rb
index 7e3ff9d844..3bb80b75e2 100644
--- a/test/fiddle/test_handle.rb
+++ b/test/fiddle/test_handle.rb
@@ -22,12 +22,14 @@ module Fiddle
     def test_static_sym_unknown
       assert_raise(DLError) { Fiddle::Handle.sym('fooo') }
       assert_raise(DLError) { Fiddle::Handle['fooo'] }
+      refute Fiddle::Handle.sym_defined?('fooo')
     end
 
     def test_static_sym
       begin
         # Linux / Darwin / FreeBSD
         refute_nil Fiddle::Handle.sym('dlopen')
+        assert Fiddle::Handle.sym_defined?('dlopen')
         assert_equal Fiddle::Handle.sym('dlopen'), Fiddle::Handle['dlopen']
         return
       rescue
@@ -54,6 +56,7 @@ module Fiddle
       handle = Fiddle::Handle.new(LIBC_SO)
       assert_raise(DLError) { handle.sym('fooo') }
       assert_raise(DLError) { handle['fooo'] }
+      refute handle.sym_defined?('fooo')
     end
 
     def test_sym_with_bad_args
@@ -66,6 +69,7 @@ module Fiddle
       handle = Handle.new(LIBC_SO)
       refute_nil handle.sym('calloc')
       refute_nil handle['calloc']
+      assert handle.sym_defined?('calloc')
     end
 
     def test_handle_close