add test

Author: IanButterworth

test/errorshow.jl

@@ -406,6 +406,8 @@ let err_str,
     @test occursin("MethodError: no method matching Bool()", err_str)
     err_str = @except_str :a() MethodError
     @test occursin("MethodError: objects of type Symbol are not callable", err_str)
+    err_str = @except_str missing(1) MethodError
+    @test occursin("MethodError: objects of type Missing are not callable", err_str)
     err_str = @except_str EightBitType() MethodError
     @test occursin("MethodError: no method matching $(curmod_prefix)EightBitType()", err_str)
     err_str = @except_str i() MethodError