Improve Gomega's representation of unexpected errors passed in to an …

…assertion

internal/assertion.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"reflect"
 
+	"github.com/onsi/gomega/format"
 	"github.com/onsi/gomega/types"
 )
 
@@ -146,7 +147,12 @@ func vetActuals(actuals []interface{}, skipIndex int) (bool, string) {
 		if actual != nil {
 			zeroValue := reflect.Zero(reflect.TypeOf(actual)).Interface()
 			if !reflect.DeepEqual(zeroValue, actual) {
-				message := fmt.Sprintf("Unexpected non-nil/non-zero argument at index %d:\n\t<%T>: %#v", i, actual, actual)
+				var message string
+				if err, ok := actual.(error); ok {
+					message = fmt.Sprintf("Unexpected error: %s\n%s", err, format.Object(err, 1))
+				} else {
+					message = fmt.Sprintf("Unexpected non-nil/non-zero argument at index %d:\n\t<%T>: %#v", i, actual, actual)
+				}
 				return false, message
 			}
 		}

internal/assertion_test.go

@@ -29,7 +29,7 @@ var _ = Describe("Making Synchronous Assertions", func() {
 				ig := NewInstrumentedGomega()
 				returnValue := ig.G.Expect(actual, extras...).To(SpecMatch(), optionalDescription...)
 				Expect(returnValue).To(Equal(expectedReturnValue))
-				Expect(ig.FailureMessage).To(Equal(expectedFailureMessage))
+				Expect(ig.FailureMessage).To(ContainSubstring(expectedFailureMessage))
 				if expectedFailureMessage != "" {
 					Expect(ig.FailureSkip).To(Equal([]int{2}))
 				}
@@ -38,7 +38,7 @@ var _ = Describe("Making Synchronous Assertions", func() {
 				ig = NewInstrumentedGomega()
 				returnValue = ig.G.ExpectWithOffset(3, actual, extras...).To(SpecMatch(), optionalDescription...)
 				Expect(returnValue).To(Equal(expectedReturnValue))
-				Expect(ig.FailureMessage).To(Equal(expectedFailureMessage))
+				Expect(ig.FailureMessage).To(ContainSubstring(expectedFailureMessage))
 				if expectedFailureMessage != "" {
 					Expect(ig.FailureSkip).To(Equal([]int{5}))
 				}
@@ -47,7 +47,7 @@ var _ = Describe("Making Synchronous Assertions", func() {
 				ig = NewInstrumentedGomega()
 				returnValue = ig.G.Ω(actual, extras...).Should(SpecMatch(), optionalDescription...)
 				Expect(returnValue).To(Equal(expectedReturnValue))
-				Expect(ig.FailureMessage).To(Equal(expectedFailureMessage))
+				Expect(ig.FailureMessage).To(ContainSubstring(expectedFailureMessage))
 				if expectedFailureMessage != "" {
 					Expect(ig.FailureSkip).To(Equal([]int{2}))
 				}
@@ -56,7 +56,7 @@ var _ = Describe("Making Synchronous Assertions", func() {
 				ig := NewInstrumentedGomega()
 				returnValue := ig.G.Expect(actual, extras...).ToNot(SpecMatch(), optionalDescription...)
 				Expect(returnValue).To(Equal(expectedReturnValue))
-				Expect(ig.FailureMessage).To(Equal(expectedFailureMessage))
+				Expect(ig.FailureMessage).To(ContainSubstring(expectedFailureMessage))
 				if expectedFailureMessage != "" {
 					Expect(ig.FailureSkip).To(Equal([]int{2}))
 				}
@@ -65,7 +65,7 @@ var _ = Describe("Making Synchronous Assertions", func() {
 				ig = NewInstrumentedGomega()
 				returnValue = ig.G.Expect(actual, extras...).NotTo(SpecMatch(), optionalDescription...)
 				Expect(returnValue).To(Equal(expectedReturnValue))
-				Expect(ig.FailureMessage).To(Equal(expectedFailureMessage))
+				Expect(ig.FailureMessage).To(ContainSubstring(expectedFailureMessage))
 				if expectedFailureMessage != "" {
 					Expect(ig.FailureSkip).To(Equal([]int{2}))
 				}
@@ -74,7 +74,7 @@ var _ = Describe("Making Synchronous Assertions", func() {
 				ig = NewInstrumentedGomega()
 				returnValue = ig.G.ExpectWithOffset(3, actual, extras...).NotTo(SpecMatch(), optionalDescription...)
 				Expect(returnValue).To(Equal(expectedReturnValue))
-				Expect(ig.FailureMessage).To(Equal(expectedFailureMessage))
+				Expect(ig.FailureMessage).To(ContainSubstring(expectedFailureMessage))
 				if expectedFailureMessage != "" {
 					Expect(ig.FailureSkip).To(Equal([]int{5}))
 				}
@@ -83,7 +83,7 @@ var _ = Describe("Making Synchronous Assertions", func() {
 				ig = NewInstrumentedGomega()
 				returnValue = ig.G.Ω(actual, extras...).ShouldNot(SpecMatch(), optionalDescription...)
 				Expect(returnValue).To(Equal(expectedReturnValue))
-				Expect(ig.FailureMessage).To(Equal(expectedFailureMessage))
+				Expect(ig.FailureMessage).To(ContainSubstring(expectedFailureMessage))
 				if expectedFailureMessage != "" {
 					Expect(ig.FailureSkip).To(Equal([]int{2}))
 				}
@@ -145,6 +145,11 @@ var _ = Describe("Making Synchronous Assertions", func() {
 			MATCH, Extras(1, "bam", struct{ Foo string }{Foo: "foo"}, nil), OptionalDescription(),
 			SHOULD_MATCH, "Unexpected non-nil/non-zero argument at index 1:\n\t<int>: 1", IT_FAILS,
 		),
+		Entry(
+			"when the matcher matches but an error is included, it fails",
+			MATCH, Extras(0, "", errors.New("welp!")), OptionalDescription(),
+			SHOULD_MATCH, "Unexpected error: welp!", IT_FAILS,
+		),
 	)
 
 	var SHOULD_OCCUR = true
@@ -191,7 +196,6 @@ var _ = Describe("Making Synchronous Assertions", func() {
 	)
 
 	When("vetting optional description parameters", func() {
-
 		It("panics when Gomega matcher is at the beginning of optional description parameters", func() {
 			ig := NewInstrumentedGomega()
 			for _, expectator := range []string{

internal/async_assertion.go

@@ -9,6 +9,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/onsi/gomega/format"
 	"github.com/onsi/gomega/types"
 )
 
@@ -164,6 +165,8 @@ func (assertion *AsyncAssertion) buildDescription(optionalDescription ...interfa
 	return fmt.Sprintf(optionalDescription[0].(string), optionalDescription[1:]...) + "\n"
 }
 
+var errInterface = reflect.TypeOf((*error)(nil)).Elem()
+
 func (assertion *AsyncAssertion) processReturnValues(values []reflect.Value) (interface{}, error, StopTryingError) {
 	var err error
 	var stopTrying StopTryingError
@@ -184,12 +187,17 @@ func (assertion *AsyncAssertion) processReturnValues(values []reflect.Value) (in
 			stopTrying = stopTryingErr
 			continue
 		}
-		zero := reflect.Zero(reflect.TypeOf(extra)).Interface()
+		extraType := reflect.TypeOf(extra)
+		zero := reflect.Zero(extraType).Interface()
 		if reflect.DeepEqual(extra, zero) {
 			continue
 		}
+		if i == len(values)-2 && extraType.Implements(errInterface) {
+			err = fmt.Errorf("function returned error: %s\n%s", extra, format.Object(extra, 1))
+			continue
+		}
 		if err == nil {
-			err = fmt.Errorf("Unexpected non-nil/non-zero argument at index %d:\n\t<%T>: %#v", i+1, extra, extra)
+			err = fmt.Errorf("Unexpected non-nil/non-zero return value at index %d:\n\t<%T>: %#v", i+1, extra, extra)
 		}
 	}
 	return actual, err, stopTrying

internal/async_assertion_test.go

@@ -508,10 +508,17 @@ var _ = Describe("Asynchronous Assertions", func() {
 					ig.G.Eventually(func() (int, string, Foo, error) {
 						return 1, "", Foo{Bar: "hi"}, nil
 					}).WithTimeout(30 * time.Millisecond).WithPolling(10 * time.Millisecond).Should(BeNumerically("<", 100))
-					Ω(ig.FailureMessage).Should(ContainSubstring("Error: Unexpected non-nil/non-zero argument at index 2:"))
+					Ω(ig.FailureMessage).Should(ContainSubstring("Error: Unexpected non-nil/non-zero return value at index 2:"))
 					Ω(ig.FailureMessage).Should(ContainSubstring(`Foo{Bar:"hi"}`))
 				})
 
+				It("has a meaningful message if all the return values are zero except the final return value, and it is an error", func() {
+					ig.G.Eventually(func() (int, string, Foo, error) {
+						return 1, "", Foo{}, errors.New("welp!")
+					}).WithTimeout(50 * time.Millisecond).WithPolling(10 * time.Millisecond).Should(BeNumerically("<", 100))
+					Ω(ig.FailureMessage).Should(ContainSubstring("Error: function returned error: welp!"))
+				})
+
 				Context("when making a ShouldNot assertion", func() {
 					It("doesn't succeed until the matcher is (not) satisfied with the first returned value _and_ all additional values are zero", func() {
 						counter, s, f, err := 0, "hi", Foo{Bar: "hi"}, errors.New("hi")
@@ -554,7 +561,7 @@ var _ = Describe("Asynchronous Assertions", func() {
 						}
 						return counter, s, f, err
 					}).WithTimeout(50 * time.Millisecond).WithPolling(10 * time.Millisecond).Should(BeNumerically("<", 100))
-					Ω(ig.FailureMessage).Should(ContainSubstring("Error: Unexpected non-nil/non-zero argument at index 2:"))
+					Ω(ig.FailureMessage).Should(ContainSubstring("Error: Unexpected non-nil/non-zero return value at index 2:"))
 					Ω(ig.FailureMessage).Should(ContainSubstring(`Foo{Bar:"welp"}`))
 					Ω(counter).Should(Equal(3))
 				})
@@ -581,7 +588,7 @@ var _ = Describe("Asynchronous Assertions", func() {
 							}
 							return counter, s, f, err
 						}).WithTimeout(50 * time.Millisecond).WithPolling(10 * time.Millisecond).ShouldNot(BeNumerically(">", 100))
-						Ω(ig.FailureMessage).Should(ContainSubstring("Error: Unexpected non-nil/non-zero argument at index 1:"))
+						Ω(ig.FailureMessage).Should(ContainSubstring("Error: Unexpected non-nil/non-zero return value at index 1:"))
 						Ω(ig.FailureMessage).Should(ContainSubstring(`<string>: "welp"`))
 						Ω(counter).Should(Equal(3))
 					})