solution: make sure eth_call works with block ref and error response

testing/README.adoc

@@ -0,0 +1,41 @@
+= Dshackle Integration Testing
+
+Test for a correct work using a simulation of different upstream behaviours and checking the Dshackle against it.
+
+.Modules:
+- `dshackle` - Dshackle config used for testing environment
+- `simple-upstream` - upstream simulator with predefines responses
+- `trial` - actual tests
+
+== How to run
+
+NOTE: Run commands in project's root dir
+
+=== Run upstream emulator
+
+[source,bash]
+----
+cd testing/simple-upstream && ./gradlew run
+----
+
+=== Run Dshackle
+
+[source,bash]
+----
+./gradlew run --args="--configPath=./testing/dshackle/dshackle.yaml"
+----
+
+or, if you want to make sure you compile and use version with your latest changes (usually unnecessary, but still):
+
+[source,bash]
+----
+./gradlew clean compileKotlin run --args="--configPath=./testing/dshackle/dshackle.yaml"
+----
+
+=== Run tests
+
+[source,bash]
+----
+cd testing/trial && ./gradlew check
+----
+

testing/simple-upstream/src/main/groovy/testing/TestcaseHandler.groovy

@@ -29,6 +29,11 @@ class TestcaseHandler implements CallHandler {
                 && params[0].toLowerCase() == "0xd949bc0fe1a5d16f4522bc47933554dcc4ada0493ff71ee1973b2410257af9fe".toLowerCase()) {
             return resourceResponse.respondWith("trace-0xd949bc.json")
         }
+        // https://github.com/emeraldpay/dshackle/issues/67
+        if (method == "eth_call"
+                && params[0].to?.toLowerCase() == "0xdAC17F958D2ee523a2206206994597C13D831ec7".toLowerCase()) {
+            return Result.error(-32000, "invalid opcode: opcode 0xfe not defined")
+        }
         return null
     }
 }

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

@@ -34,4 +34,21 @@ class GivesErrorSpec extends Specification {
         }
     }
 
+    def "Dispatch error from upstream when block is specified"() {
+        // issue #67
+        when:
+        def call = [
+                to  : "0xdAC17F958D2ee523a2206206994597C13D831ec7",
+                from: "0xEF65ffB384c99a00403EAa22115323a555700D79",
+                data: "0xa9059cbb0000000000000000000000003f5ce5fbfe3e9af3971dd833d26ba9b5c936f0be000000000000000000000000000000000000000000000000000000004856fb60"
+        ]
+        def act = client.execute("eth_call", [call, "0x100000"])
+        then:
+        act.result == null
+        act.error != null
+        with(act.error) {
+            code == -32000
+            message == "invalid opcode: opcode 0xfe not defined"
+        }
+    }
 }