diff --git a/README.md b/README.md
index be923cf..eb3cb62 100644
--- a/README.md
+++ b/README.md
@@ -181,8 +181,6 @@ this case since the response has been already arrived (we are inside the callbac
   // ... your code can continue here without any delay
 ```
 
-## etcd operations
-
 ### Multiple endpoints
 
 Connecting to multiple endpoints is supported:
@@ -364,6 +362,46 @@ Note that the timeout value is the "timeout" when waiting for responses upon the
 It doesn't means the timeout between issuing a `.set()` method getting the `etcd::Response`, as in the async mode the such a time
 duration is unpredictable and the gRPC timeout should be enough to avoid deadly waiting (e.g., waiting for a `lock()`).
 
+### Error code in responses
+
+The `class etcd::Response` may yield an error code and error message when error occurs,
+
+```cpp
+  int error_code() const;
+  std::string const & error_message() const;
+
+  bool is_ok() const;
+```
+
+The error code would be `0` when succeed, otherwise the error code might be
+
+```cpp
+  extern const int ERROR_GRPC_OK;
+  extern const int ERROR_GRPC_CANCELLED;
+  extern const int ERROR_GRPC_UNKNOWN;
+  extern const int ERROR_GRPC_INVALID_ARGUMENT;
+  extern const int ERROR_GRPC_DEADLINE_EXCEEDED;
+  extern const int ERROR_GRPC_NOT_FOUND;
+  extern const int ERROR_GRPC_ALREADY_EXISTS;
+  extern const int ERROR_GRPC_PERMISSION_DENIED;
+  extern const int ERROR_GRPC_UNAUTHENTICATED;
+  extern const int ERROR_GRPC_RESOURCE_EXHAUSTED;
+  extern const int ERROR_GRPC_FAILED_PRECONDITION;
+  extern const int ERROR_GRPC_ABORTED;
+  extern const int ERROR_GRPC_OUT_OF_RANGE;
+  extern const int ERROR_GRPC_UNIMPLEMENTED;
+  extern const int ERROR_GRPC_INTERNAL;
+  extern const int ERROR_GRPC_UNAVAILABLE;
+  extern const int ERROR_GRPC_DATA_LOSS;
+
+  extern const int ERROR_KEY_NOT_FOUND;
+  extern const int ERROR_COMPARE_FAILED;
+  extern const int ERROR_KEY_ALREADY_EXISTS;
+  extern const int ERROR_ACTION_CANCELLED;
+```
+
+## Etcd operations
+
 ### Reading a value
 
 You can read a value with the `get()` method of the client instance. The only parameter is the
@@ -434,7 +472,7 @@ some specific conditions.
 
 * `add(key, value)` creates a new value if it's key does not exists and returns a "Key
   already exists" error otherwise (error code `ERROR_KEY_ALREADY_EXISTS`)
-* `modify(key, value)` modifies an already existing value or returns a "Key not found" error
+* `modify(key, value)` modifies an already existing value or returns a "etcd-cpp-apiv3: key not found" error
   otherwise (error code `KEY_NOT_FOUND`)
 * `modify_if(key, value, old_value)` modifies an already existing value but only if the previous
   value equals with old_value. If the values does not match returns with "Compare failed" error
diff --git a/etcd/Client.hpp b/etcd/Client.hpp
index 174a869..8554ef1 100644
--- a/etcd/Client.hpp
+++ b/etcd/Client.hpp
@@ -16,7 +16,6 @@
 
 namespace etcd
 {
-  // FIXME
   /**
    * Client is responsible for maintaining a connection towards an etcd server.
    * Etcd operations can be reached via the methods of the client.
diff --git a/etcd/Response.hpp b/etcd/Response.hpp
index 56b9b26..5f4384e 100644
--- a/etcd/Response.hpp
+++ b/etcd/Response.hpp
@@ -63,9 +63,9 @@ namespace etcd
     }
 
     template <typename T>
-    static etcd::Response create(std::function<std::unique_ptr<T>()> callfn)
+    static etcd::Response create(std::function<std::unique_ptr<T>()> fn)
     {
-        auto call = callfn();
+        auto call = fn();
 
         call->waitForResponse();
         auto v3resp = call->ParseResponse();
@@ -76,9 +76,9 @@ namespace etcd
     }
 
     template <typename T>
-    static etcd::Response create(std::function<std::shared_ptr<T>()> callfn)
+    static etcd::Response create(std::function<std::shared_ptr<T>()> fn)
     {
-        auto call = callfn();
+        auto call = fn();
 
         call->waitForResponse();
         auto v3resp = call->ParseResponse();
@@ -92,6 +92,16 @@ namespace etcd
 
     Response(const Response &);
 
+    /**
+     * Returns the error code received from the etcd server. In case of success the error code is 0.
+     */
+    int error_code() const;
+
+    /**
+     * Returns the string representation of the error code
+     */
+    std::string const & error_message() const;
+
     /**
      * Returns true if this is a successful response
      */
@@ -102,21 +112,11 @@ namespace etcd
      */
     bool is_network_unavailable() const;
 
-    /**
-     * Returns the error code received from the etcd server. In case of success the error code is 0.
-     */
-    int error_code() const;
-
     /**
      * Check whether the response contains a grpc TIMEOUT error.
      */
     bool is_grpc_timeout() const;
 
-    /**
-     * Returns the string representation of the error code
-     */
-    std::string const & error_message() const;
-
     /**
      * Returns the action type of the operation that this response belongs to.
      */
@@ -200,6 +200,7 @@ namespace etcd
 
   protected:
     Response(const etcdv3::V3Response& response, std::chrono::microseconds const& duration);
+    Response(int error_code, std::string const& error_message);
     Response(int error_code, char const * error_message);
 
     int         _error_code;
diff --git a/etcd/SyncClient.hpp b/etcd/SyncClient.hpp
index aaa8840..30e6cef 100644
--- a/etcd/SyncClient.hpp
+++ b/etcd/SyncClient.hpp
@@ -68,7 +68,6 @@ namespace etcd
   class Watcher;
   class Client;
 
-  // FIXME
   /**
    * Client is responsible for maintaining a connection towards an etcd server.
    * Etcd operations can be reached via the methods of the client.
diff --git a/etcd/v3/action_constants.hpp b/etcd/v3/action_constants.hpp
index 8c4d29a..d1728a4 100644
--- a/etcd/v3/action_constants.hpp
+++ b/etcd/v3/action_constants.hpp
@@ -41,6 +41,24 @@ namespace etcdv3
 
   extern char const * ELECTION_OBSERVE_CREATE;
 
+  extern const int ERROR_GRPC_OK;
+  extern const int ERROR_GRPC_CANCELLED;
+  extern const int ERROR_GRPC_UNKNOWN;
+  extern const int ERROR_GRPC_INVALID_ARGUMENT;
+  extern const int ERROR_GRPC_DEADLINE_EXCEEDED;
+  extern const int ERROR_GRPC_NOT_FOUND;
+  extern const int ERROR_GRPC_ALREADY_EXISTS;
+  extern const int ERROR_GRPC_PERMISSION_DENIED;
+  extern const int ERROR_GRPC_UNAUTHENTICATED;
+  extern const int ERROR_GRPC_RESOURCE_EXHAUSTED;
+  extern const int ERROR_GRPC_FAILED_PRECONDITION;
+  extern const int ERROR_GRPC_ABORTED;
+  extern const int ERROR_GRPC_OUT_OF_RANGE;
+  extern const int ERROR_GRPC_UNIMPLEMENTED;
+  extern const int ERROR_GRPC_INTERNAL;
+  extern const int ERROR_GRPC_UNAVAILABLE;
+  extern const int ERROR_GRPC_DATA_LOSS;
+
   extern const int ERROR_KEY_NOT_FOUND;
   extern const int ERROR_COMPARE_FAILED;
   extern const int ERROR_KEY_ALREADY_EXISTS;
diff --git a/src/Response.cpp b/src/Response.cpp
index f485fbf..6b8365b 100644
--- a/src/Response.cpp
+++ b/src/Response.cpp
@@ -67,6 +67,13 @@ etcd::Response::Response(const etcdv3::V3Response& reply, std::chrono::microseco
   _raft_term = reply.get_raft_term();
 }
 
+etcd::Response::Response(int error_code, std::string const& error_message)
+  : _error_code(error_code),
+    _error_message(error_message),
+    _index(0)
+{
+}
+
 etcd::Response::Response(int error_code, char const * error_message)
   : _error_code(error_code),
     _error_message(error_message),
@@ -84,21 +91,6 @@ std::string const & etcd::Response::error_message() const
   return _error_message;
 }
 
-bool etcd::Response::is_grpc_timeout() const
-{
-  return _error_code == grpc::StatusCode::DEADLINE_EXCEEDED;
-}
-
-int64_t etcd::Response::index() const
-{
-  return _index;
-}
-
-std::string const & etcd::Response::action() const
-{
-  return _action;
-}
-
 bool etcd::Response::is_ok() const
 {
   return error_code() == 0;
@@ -109,6 +101,21 @@ bool etcd::Response::is_network_unavailable() const
   return error_code() == ::grpc::StatusCode::UNAVAILABLE;
 }
 
+bool etcd::Response::is_grpc_timeout() const
+{
+  return _error_code == grpc::StatusCode::DEADLINE_EXCEEDED;
+}
+
+std::string const & etcd::Response::action() const
+{
+  return _action;
+}
+
+int64_t etcd::Response::index() const
+{
+  return _index;
+}
+
 etcd::Value const & etcd::Response::value() const
 {
   return _value;
diff --git a/src/SyncClient.cpp b/src/SyncClient.cpp
index d8f193f..76ec094 100644
--- a/src/SyncClient.cpp
+++ b/src/SyncClient.cpp
@@ -530,7 +530,7 @@ etcd::Response etcd::SyncClient::set(std::string const & key, std::string const
     auto res = this->leasegrant(ttl);
     if(!res.is_ok()) 
     {
-      return etcd::Response(res.error_code(), res.error_message().c_str());    
+      return etcd::Response(res.error_code(), res.error_message());
     }
     else
     {
@@ -565,7 +565,7 @@ etcd::Response etcd::SyncClient::add(std::string const & key, std::string const
     auto res = this->leasegrant(ttl);
     if(!res.is_ok()) 
     {
-      return etcd::Response(res.error_code(), res.error_message().c_str());    
+      return etcd::Response(res.error_code(), res.error_message());
     }
     else
     {
@@ -614,7 +614,7 @@ etcd::Response etcd::SyncClient::modify(std::string const & key, std::string con
     auto res = leasegrant(ttl);
     if(!res.is_ok()) 
     {
-        return etcd::Response(res.error_code(), res.error_message().c_str());    
+        return etcd::Response(res.error_code(), res.error_message());
     }
     else
     {
@@ -649,7 +649,7 @@ etcd::Response etcd::SyncClient::modify_if(std::string const & key, std::string
     auto res = leasegrant(ttl);
     if(!res.is_ok()) 
     {
-        return etcd::Response(res.error_code(), res.error_message().c_str());    
+        return etcd::Response(res.error_code(), res.error_message());
     }
     else
     {
@@ -673,7 +673,7 @@ etcd::Response etcd::SyncClient::modify_if(std::string const & key, std::string
     auto res = leasegrant(ttl);
     if(!res.is_ok()) 
     {
-        return etcd::Response(res.error_code(), res.error_message().c_str());    
+        return etcd::Response(res.error_code(), res.error_message());
     }
     else
     {
diff --git a/src/v3/AsyncCompareAndDeleteAction.cpp b/src/v3/AsyncCompareAndDeleteAction.cpp
index 1045709..f4253d4 100644
--- a/src/v3/AsyncCompareAndDeleteAction.cpp
+++ b/src/v3/AsyncCompareAndDeleteAction.cpp
@@ -51,7 +51,7 @@ etcdv3::AsyncTxnResponse etcdv3::AsyncCompareAndDeleteAction::ParseResponse()
     if(!reply.succeeded())
     {
       txn_resp.set_error_code(ERROR_COMPARE_FAILED);
-      txn_resp.set_error_message("Compare failed");
+      txn_resp.set_error_message("etcd-cpp-apiv3: compare failed");
     } 
   }
     
diff --git a/src/v3/AsyncCompareAndSwapAction.cpp b/src/v3/AsyncCompareAndSwapAction.cpp
index 43e9b69..82d003d 100644
--- a/src/v3/AsyncCompareAndSwapAction.cpp
+++ b/src/v3/AsyncCompareAndSwapAction.cpp
@@ -53,7 +53,7 @@ etcdv3::AsyncTxnResponse etcdv3::AsyncCompareAndSwapAction::ParseResponse()
     if(!reply.succeeded() && !txn_resp.get_error_code())
     {
       txn_resp.set_error_code(ERROR_COMPARE_FAILED);
-      txn_resp.set_error_message("Compare failed");
+      txn_resp.set_error_message("etcd-cpp-apiv3: compare failed");
     } 
   }
     
diff --git a/src/v3/AsyncDeleteResponse.cpp b/src/v3/AsyncDeleteResponse.cpp
index fa4b3d3..f504e3a 100644
--- a/src/v3/AsyncDeleteResponse.cpp
+++ b/src/v3/AsyncDeleteResponse.cpp
@@ -9,7 +9,7 @@ void etcdv3::AsyncDeleteResponse::ParseResponse(std::string const& key, bool pre
   if(resp.prev_kvs_size() == 0)
   {
     error_code = etcdv3::ERROR_KEY_NOT_FOUND;
-    error_message = "Key not found";
+    error_message = "etcd-cpp-apiv3: key not found";
   }
   else
   {
diff --git a/src/v3/AsyncRangeResponse.cpp b/src/v3/AsyncRangeResponse.cpp
index b3ab92e..2dfa73b 100644
--- a/src/v3/AsyncRangeResponse.cpp
+++ b/src/v3/AsyncRangeResponse.cpp
@@ -8,7 +8,7 @@ void etcdv3::AsyncRangeResponse::ParseResponse(RangeResponse& resp, bool prefix)
   if(resp.kvs_size() == 0 && !prefix)
   {
     error_code = etcdv3::ERROR_KEY_NOT_FOUND;
-    error_message = "Key not found";
+    error_message = "etcd-cpp-apiv3: key not found";
     return;
   }
   else
diff --git a/src/v3/AsyncSetAction.cpp b/src/v3/AsyncSetAction.cpp
index 9ae2c29..e09c023 100644
--- a/src/v3/AsyncSetAction.cpp
+++ b/src/v3/AsyncSetAction.cpp
@@ -44,7 +44,7 @@ etcdv3::AsyncTxnResponse etcdv3::AsyncSetAction::ParseResponse()
     if(!reply.succeeded() && isCreate)
     {
       txn_resp.set_error_code(etcdv3::ERROR_KEY_ALREADY_EXISTS);
-      txn_resp.set_error_message("Key already exists");
+      txn_resp.set_error_message("etcd-cpp-apiv3: key already exists");
     } 
   }
   return txn_resp;
diff --git a/src/v3/AsyncTxnAction.cpp b/src/v3/AsyncTxnAction.cpp
index ef1b116..6d2d07c 100644
--- a/src/v3/AsyncTxnAction.cpp
+++ b/src/v3/AsyncTxnAction.cpp
@@ -30,7 +30,7 @@ etcdv3::AsyncTxnResponse etcdv3::AsyncTxnAction::ParseResponse()
     if(!reply.succeeded() && !txn_resp.get_error_code())
     {
       txn_resp.set_error_code(ERROR_COMPARE_FAILED);
-      txn_resp.set_error_message("compare failed");
+      txn_resp.set_error_message("etcd-cpp-apiv3: compare failed");
     } 
   }
     
diff --git a/src/v3/AsyncUpdateAction.cpp b/src/v3/AsyncUpdateAction.cpp
index 587b3fe..00ff7bc 100644
--- a/src/v3/AsyncUpdateAction.cpp
+++ b/src/v3/AsyncUpdateAction.cpp
@@ -43,7 +43,7 @@ etcdv3::AsyncTxnResponse etcdv3::AsyncUpdateAction::ParseResponse()
     else
     {
       txn_resp.set_error_code(etcdv3::ERROR_KEY_NOT_FOUND);
-      txn_resp.set_error_message("Key not found");
+      txn_resp.set_error_message("etcd-cpp-apiv3: key not found");
     }
   }
   return txn_resp;
diff --git a/src/v3/action_constants.cpp b/src/v3/action_constants.cpp
index 2baa6cf..a212ffe 100644
--- a/src/v3/action_constants.cpp
+++ b/src/v3/action_constants.cpp
@@ -40,6 +40,24 @@ char const * etcdv3::WATCH_WRITES_DONE = "watch writes done";
 
 char const * etcdv3::ELECTION_OBSERVE_CREATE = "observe create";
 
+const int etcdv3::ERROR_GRPC_OK = 0;
+const int etcdv3::ERROR_GRPC_CANCELLED = 1;
+const int etcdv3::ERROR_GRPC_UNKNOWN = 2;
+const int etcdv3::ERROR_GRPC_INVALID_ARGUMENT = 3;
+const int etcdv3::ERROR_GRPC_DEADLINE_EXCEEDED = 4;
+const int etcdv3::ERROR_GRPC_NOT_FOUND = 5;
+const int etcdv3::ERROR_GRPC_ALREADY_EXISTS = 6;
+const int etcdv3::ERROR_GRPC_PERMISSION_DENIED = 7;
+const int etcdv3::ERROR_GRPC_UNAUTHENTICATED = 16;
+const int etcdv3::ERROR_GRPC_RESOURCE_EXHAUSTED = 8;
+const int etcdv3::ERROR_GRPC_FAILED_PRECONDITION = 9;
+const int etcdv3::ERROR_GRPC_ABORTED = 10;
+const int etcdv3::ERROR_GRPC_OUT_OF_RANGE = 11;
+const int etcdv3::ERROR_GRPC_UNIMPLEMENTED = 12;
+const int etcdv3::ERROR_GRPC_INTERNAL = 13;
+const int etcdv3::ERROR_GRPC_UNAVAILABLE = 14;
+const int etcdv3::ERROR_GRPC_DATA_LOSS = 15;
+
 const int etcdv3::ERROR_KEY_NOT_FOUND = 100;
 const int etcdv3::ERROR_COMPARE_FAILED = 101;
 const int etcdv3::ERROR_KEY_ALREADY_EXISTS = 105;
diff --git a/tst/AuthTest.cpp b/tst/AuthTest.cpp
index 9efc91f..8862688 100644
--- a/tst/AuthTest.cpp
+++ b/tst/AuthTest.cpp
@@ -29,7 +29,7 @@ TEST_CASE("add a new key after authenticate")
   CHECK(0 < resp.index());
   CHECK(etcd::ERROR_KEY_ALREADY_EXISTS == etcd->add("/test/key1", "43").get().error_code()); // Key already exists
   CHECK(etcd::ERROR_KEY_ALREADY_EXISTS == etcd->add("/test/key1", "42").get().error_code()); // Key already exists
-  CHECK("Key already exists" == etcd->add("/test/key1", "42").get().error_message());
+  CHECK("etcd-cpp-apiv3: key already exists" == etcd->add("/test/key1", "42").get().error_message());
 }
 
 TEST_CASE("read a value from etcd")
diff --git a/tst/EtcdTest.cpp b/tst/EtcdTest.cpp
index 13e483e..ca99497 100644
--- a/tst/EtcdTest.cpp
+++ b/tst/EtcdTest.cpp
@@ -31,7 +31,7 @@ TEST_CASE("add a new key")
   CHECK(0 < resp.index());
   CHECK(etcd::ERROR_KEY_ALREADY_EXISTS == etcd.add("/test/key1", "43").get().error_code()); // Key already exists
   CHECK(etcd::ERROR_KEY_ALREADY_EXISTS == etcd.add("/test/key1", "42").get().error_code()); // Key already exists
-  CHECK("Key already exists" == etcd.add("/test/key1", "42").get().error_message());
+  CHECK("etcd-cpp-apiv3: key already exists" == etcd.add("/test/key1", "42").get().error_message());
 }
 
 TEST_CASE("read a value from etcd")
@@ -98,13 +98,13 @@ TEST_CASE("atomic compare-and-swap")
   res = etcd.modify_if("/test/key1", "44", "42").get();
   CHECK(!res.is_ok());
   CHECK(etcd::ERROR_COMPARE_FAILED == res.error_code());
-  CHECK("Compare failed" == res.error_message());
+  CHECK("etcd-cpp-apiv3: compare failed" == res.error_message());
 
   // modify fails the second time
   res = etcd.modify_if("/test/key222", "44", "42").get();
   CHECK(!res.is_ok());
   CHECK(etcd::ERROR_KEY_NOT_FOUND == res.error_code());
-  CHECK("Key not found" == res.error_message());
+  CHECK("etcd-cpp-apiv3: key not found" == res.error_message());
 }
 
 TEST_CASE("delete a value")
@@ -113,7 +113,7 @@ TEST_CASE("delete a value")
   etcd::Response resp = etcd.rm("/test/key11111").get();
   CHECK(!resp.is_ok());
   CHECK(etcd::ERROR_KEY_NOT_FOUND == resp.error_code());
-  CHECK("Key not found" == resp.error_message());
+  CHECK("etcd-cpp-apiv3: key not found" == resp.error_message());
 
   int64_t index = etcd.get("/test/key1").get().index();
   int64_t create_index = etcd.get("/test/key1").get().value().created_index();
@@ -145,7 +145,7 @@ TEST_CASE("atomic compare-and-delete based on prevValue")
   etcd::Response res = etcd.rm_if("/test/key1", "43").get();
   CHECK(!res.is_ok());
   CHECK(etcd::ERROR_COMPARE_FAILED == res.error_code());
-  CHECK("Compare failed" == res.error_message());
+  CHECK("etcd-cpp-apiv3: compare failed" == res.error_message());
 
   res = etcd.rm_if("/test/key1", "42").get();
   REQUIRE(res.is_ok());
@@ -161,7 +161,7 @@ TEST_CASE("atomic compare-and-delete based on prevIndex")
   etcd::Response res = etcd.rm_if("/test/key1", index - 1).get();
   CHECK(!res.is_ok());
   CHECK(etcd::ERROR_COMPARE_FAILED == res.error_code());
-  CHECK("Compare failed" == res.error_message());
+  CHECK("etcd-cpp-apiv3: compare failed" == res.error_message());
 
   res = etcd.rm_if("/test/key1", index).get();
   REQUIRE(res.is_ok());
@@ -185,7 +185,7 @@ TEST_CASE("deep atomic compare-and-swap")
   res = etcd.modify_if("/test/key1", "44", "42").get();
   CHECK(!res.is_ok());
   CHECK(etcd::ERROR_COMPARE_FAILED == res.error_code());
-  CHECK("Compare failed" == res.error_message());
+  CHECK("etcd-cpp-apiv3: compare failed" == res.error_message());
 
   // succes with the correct index
   res = etcd.modify_if("/test/key1", "44", index).get();
@@ -197,7 +197,7 @@ TEST_CASE("deep atomic compare-and-swap")
   res = etcd.modify_if("/test/key1", "45", index).get();
   CHECK(!res.is_ok());
   CHECK(etcd::ERROR_COMPARE_FAILED == res.error_code());
-  CHECK("Compare failed" == res.error_message());
+  CHECK("etcd-cpp-apiv3: compare failed" == res.error_message());
 }
 
 TEST_CASE("list a directory")
@@ -295,12 +295,12 @@ TEST_CASE("delete a directory")
   resp = etcd.rmdir("/test/dirnotfound", true).get();
   CHECK(!resp.is_ok());
   CHECK(etcd::ERROR_KEY_NOT_FOUND == resp.error_code());
-  CHECK("Key not found" == resp.error_message());
+  CHECK("etcd-cpp-apiv3: key not found" == resp.error_message());
 
   resp = etcd.rmdir("/test/new_dir", false).get();
   CHECK(!resp.is_ok());
   CHECK(etcd::ERROR_KEY_NOT_FOUND == resp.error_code());
-  CHECK("Key not found" == resp.error_message());
+  CHECK("etcd-cpp-apiv3: key not found" == resp.error_message());
 }
 
 TEST_CASE("delete by range")
diff --git a/tst/SecurityChannelTest.cpp b/tst/SecurityChannelTest.cpp
index fda754e..89001d7 100644
--- a/tst/SecurityChannelTest.cpp
+++ b/tst/SecurityChannelTest.cpp
@@ -32,7 +32,7 @@ TEST_CASE("add a new key after authenticate")
   CHECK(0 < resp.index());
   CHECK(etcd::ERROR_KEY_ALREADY_EXISTS == etcd->add("/test/key1", "43").get().error_code()); // Key already exists
   CHECK(etcd::ERROR_KEY_ALREADY_EXISTS == etcd->add("/test/key1", "42").get().error_code()); // Key already exists
-  CHECK("Key already exists" == etcd->add("/test/key1", "42").get().error_message());
+  CHECK("etcd-cpp-apiv3: key already exists" == etcd->add("/test/key1", "42").get().error_message());
 }
 
 TEST_CASE("read a value from etcd")