solution: integration test with two upstreams

testing/trial/src/main/groovy/io/emeraldpay/dshackle/testing/trial/ProxyClient.groovy

@@ -28,6 +28,10 @@ class ProxyClient {
         return new ProxyClient("http://127.0.0.1:18080/$prefix")
     }
 
+    static ProxyClient forOriginal(int port) {
+        return new ProxyClient("http://127.0.0.1:$port")
+    }
+
     Map<String, Object> execute(String method, List<Object> params) {
         return execute(sequence++, method, params)
     }

testing/trial/src/test/groovy/io/emeraldpay/dshackle/testing/trial/proxy/DispatchSpec.groovy

@@ -0,0 +1,40 @@
+package io.emeraldpay.dshackle.testing.trial.proxy
+
+import io.emeraldpay.dshackle.testing.trial.ProxyClient
+import spock.lang.Specification
+
+class DispatchSpec extends Specification {
+
+    def client = ProxyClient.forPrefix("eth")
+
+    def "multiple calls routed roughly equal to upstreams"() {
+        when:
+        def calls1before = ProxyClient.forOriginal(18545).execute("eth_call", [[to: "0x0123456789abcdef0123456789abcdef00000002"]]).result as List
+        def calls2before = ProxyClient.forOriginal(18546).execute("eth_call", [[to: "0x0123456789abcdef0123456789abcdef00000002"]]).result as List
+
+        100.times {
+            client.execute("eth_call", [[to: "0x0123456789abcdef0123456789abcdef00000001", data: "0x00000000" + Integer.toString(it, 16)]])
+        }
+
+        def calls1after = ProxyClient.forOriginal(18545).execute("eth_call", [[to: "0x0123456789abcdef0123456789abcdef00000002"]]).result as List
+        def calls2after = ProxyClient.forOriginal(18546).execute("eth_call", [[to: "0x0123456789abcdef0123456789abcdef00000002"]]).result as List
+
+        def calls1 = onlyNew(calls1before, calls1after)
+        def calls2 = onlyNew(calls2before, calls2after)
+
+        then:
+        calls1.size() >= 48
+        calls2.size() >= 48
+        calls1.size() + calls2.size() == 100
+    }
+
+    private List onlyNew(List before, List after) {
+        return after.findAll { a ->
+            !before.any { b ->
+                b.id == a.id
+            }
+        }.findAll {
+            (it.json as String).contains("0x0123456789abcdef0123456789abcdef00000001")
+        }
+    }
+}