Add unit tests for emitting error code/type in tracing (#904)

* Add unit tests for emitting error code/type in tracing

* Make tests table driven

* Update inbound_internal_test.go to address review comments

* Update inbound.go to fix comment

* Address review comments

inbound.go

@@ -423,8 +423,8 @@ func (response *InboundCallResponse) doneSending() {
 			errorType := appErrorType
 			if response.systemError {
 				errorType = systemErrorType
-				// if the error is a system error, set the error code in span log
-				span.SetTag("rpc.tchannel.system_error_code", GetSystemErrorCode(response.err))
+				// if the error is a system error, set the error code as a span tag
+				span.SetTag("rpc.tchannel.system_error_code", GetSystemErrorCode(response.err).MetricsKey())
 			}
 			span.SetTag("rpc.tchannel.error_type", errorType)
 		}

inbound_internal_test.go

@@ -0,0 +1,113 @@
+// Copyright (c) 2015 Uber Technologies, Inc.
+
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package tchannel
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/opentracing/opentracing-go/mocktracer"
+	"github.com/stretchr/testify/assert"
+)
+
+type statsReporter struct{}
+
+func (w *statsReporter) IncCounter(name string, tags map[string]string, value int64) {
+}
+
+func (w *statsReporter) UpdateGauge(name string, tags map[string]string, value int64) {
+}
+
+func (w *statsReporter) RecordTimer(name string, tags map[string]string, d time.Duration) {
+}
+
+type testCase struct {
+	name                   string
+	injectedError          error
+	systemError            bool
+	applicationError       bool
+	expectedSpanError      bool
+	expectedSpanErrorType  string
+	expectedSystemErrorKey string
+}
+
+func TestTracingSpanError(t *testing.T) {
+	var (
+		systemError      = NewSystemError(ErrCodeBusy, "foo")
+		applicationError = fmt.Errorf("application")
+	)
+
+	testCases := []testCase{
+		{
+			name:                   "ApplicationError",
+			injectedError:          applicationError,
+			systemError:            false,
+			applicationError:       true,
+			expectedSpanError:      true,
+			expectedSpanErrorType:  "application",
+			expectedSystemErrorKey: "",
+		},
+		{
+			name:                   "SystemError",
+			injectedError:          systemError,
+			systemError:            true,
+			applicationError:       false,
+			expectedSpanError:      true,
+			expectedSpanErrorType:  "system",
+			expectedSystemErrorKey: GetSystemErrorCode(systemError).MetricsKey(),
+		},
+	}
+
+	for _, tt := range testCases {
+		t.Run(tt.name, func(t *testing.T) {
+
+			var (
+				parsedSpan *mocktracer.MockSpan
+
+				tracer   = mocktracer.New()
+				callResp = &InboundCallResponse{
+					span:          tracer.StartSpan("test"),
+					statsReporter: &statsReporter{},
+					reqResWriter: reqResWriter{
+						err: tt.injectedError,
+					},
+					applicationError: tt.applicationError,
+					systemError:      tt.systemError,
+					timeNow:          time.Now,
+					cancel:           func() {},
+				}
+			)
+
+			callResp.doneSending()
+
+			parsedSpan = callResp.span.(*mocktracer.MockSpan)
+
+			assert.Equal(t, tt.expectedSpanError, parsedSpan.Tag("error").(bool))
+			if tt.expectedSystemErrorKey == "" {
+				assert.Nil(t, parsedSpan.Tag("rpc.tchannel.system_error_code"))
+			} else {
+				assert.Equal(t, tt.expectedSystemErrorKey, parsedSpan.Tag("rpc.tchannel.system_error_code").(string))
+			}
+			assert.Equal(t, tt.expectedSpanErrorType, parsedSpan.Tag("rpc.tchannel.error_type").(string))
+		})
+	}
+}