In https://github.com/mongodb/specifications/blob/master/source/read-write-concern/tests/connection-string/write-concern.yml#L25, there is a test which requres that a wTimeoutMS of -500 is treated as an invalid uri:

        description: "wtimeoutMS as an invalid number"
        uri: "mongodb://localhost/?wtimeoutMS=-500"
        valid: false
        warning: ~

A search through specifications repo found only the uri options specification defining wTimeoutMS behavior (https://github.com/mongodb/specifications/blob/master/source/uri-options/uri-options.rst#list-of-specified-options), where wTimeoutMS is defined to be a "non-negative integer", however the corresponding test (https://github.com/mongodb/specifications/blob/master/source/uri-options/tests/concern-options.yml#L40) specifies that a negative value of wTimeoutMS produces a warning and a valid uri:

        description: "Too low wTimeoutMS causes a warning"
        uri: "mongodb://example.com/?wTimeoutMS=-2"
        valid: true
        warning: true
        hosts: ~
        auth: ~
        options: {}

I propose that the read/write concern test is updated to be in line with uri specification language and tests.