simple.vcl

varnishtest "Cache busting test"
 server s1 {
       rxreq
       expect req.url == "/foo/svc.json?api-key=abc%20qwer1234&another=value&name=value"
       txresp
} -start
varnish v1 -vcl+backend {
    import std;
    sub vcl_recv {
        if (req.url ~ "_=[0-9]+") {
            set req.http.clean = regsuball(req.url, "(_=[0-9]+)", "");
            set req.http.clean = regsub(req.http.clean, "\?&", "?");
            set req.http.clean = regsub(req.http.clean, "&&",  "&");
            set req.http.clean = regsub(req.http.clean, "&$",  "");
            set req.http.clean = regsub(req.http.clean, "\?$", "");
            set req.url = req.http.clean;
        }
    }
    sub vcl_deliver {
        set resp.http.clean = req.http.clean;
    }
} -start
client c1 {
    txreq -url "/foo/svc.json?api-key=abc%20qwer1234&another=value&_=123412341234&name=value&_=12341234"
    rxresp
    expect resp.http.clean == "/foo/svc.json?api-key=abc%20qwer1234&another=value&name=value"
}
client c1 -run