code: def test_dtype_instances(backend_fw):
      with BackendHandler.update_backend(backend_fw) as ivy_backend:
          assert ivy_backend.exists(ivy_backend.int8)
          assert ivy_backend.exists(ivy_backend.int16)
          assert ivy_backend.exists(ivy_backend.int32)
          assert ivy_backend.exists(ivy_backend.int64)
          assert ivy_backend.exists(ivy_backend.uint8)
          if backend_fw not in ["torch", "paddle", "mxnet"]:
              assert ivy_backend.exists(ivy_backend.uint16)
              assert ivy_backend.exists(ivy_backend.uint32)
              assert ivy_backend.exists(ivy_backend.uint64)
          assert ivy_backend.exists(ivy_backend.float32)
          assert ivy_backend.exists(ivy_backend.float64)
          assert ivy_backend.exists(ivy_backend.complex64)
          assert ivy_backend.exists(ivy_backend.complex128)
          assert ivy_backend.exists(ivy_backend.bool)
  
imports: import numpy
  from hypothesis import strategies
  import typing
  import ivy
  import ivy_tests.test_ivy.helpers
  from ivy_tests.test_ivy.helpers import handle_test, BackendHandler
label_desc: Use image node_id 21 for calling a global function with example usage: test_dtype_instances(backend_fw) without return types