测试异常

运行测试时遇到的异常将导致测试失败，如果测试不在测试集中，则终止测试引擎。通常，这是一件好事，因为在大多数情况下，异常并不是理想的结果。但有时候，人们想要特别测试是否会引发某种异常。@test_throws 宏有利于此。

julia> @test_throws BoundsError [1, 2, 3][4]
Test Passed
  Expression: ([1,2,3])[4]
      Thrown: BoundsError

如果抛出了错误的异常，@test_throws 仍然会失败：

julia> @test_throws TypeError [1, 2, 3][4]
Test Failed
  Expression: ([1,2,3])[4]
    Expected: TypeError
      Thrown: BoundsError
ERROR: There was an error during testing
 in record(::Base.Test.FallbackTestSet, ::Base.Test.Fail) at ./test.jl:397
 in do_test_throws(::Base.Test.Threw, ::Expr, ::Type{T}) at ./test.jl:329

如果没有抛出异常，@test_throws 也会失败：

julia> @test_throws BoundsError [1, 2, 3, 4][4]
Test Failed
  Expression: ([1,2,3,4])[4]
    Expected: BoundsError
  No exception thrown
ERROR: There was an error during testing
 in record(::Base.Test.FallbackTestSet, ::Base.Test.Fail) at ./test.jl:397
 in do_test_throws(::Base.Test.Returned, ::Expr, ::Type{T}) at ./test.jl:329