ExactError, asserts that err is not nil and its string matches

assert/assertions.go

@@ -469,3 +469,22 @@ func Error(t TestingT, theError error, msgAndArgs ...interface{}) bool {
 	return NotNil(t, theError, "An error is expected but got nil. %s", message)
 
 }
+
+// Error asserts that a function returned an error (i.e. not `nil`).
+//
+//   actualObj, err := SomeFunction()
+//   if assert.Error(t, err, "An error was expected") {
+//	   assert.Equal(t, err, expectedError)
+//   }
+//
+// Returns whether the assertion was successful (true) or not (false).
+func ExactError(t TestingT, theError error, errString string, msgAndArgs ...interface{}) bool {
+
+	message := messageFromMsgAndArgs(msgAndArgs...)
+	if !NotNil(t, theError, "An error is expected but got nil. %s", message) {
+		return false
+	}
+	s := "An error with value \"%s\" is expected but got \"%s\". %s"
+	return Equal(t, theError.Error(), errString,
+		s, errString, theError.Error(), message)
+}

assert/assertions_test.go

@@ -311,6 +311,22 @@ func TestError(t *testing.T) {
 
 }
 
+func TestExactError(t *testing.T) {
+	mockT := new(testing.T)
+
+	// start with a nil error
+	var err error = nil
+	False(t, ExactError(mockT, err, ""),
+		"ExactError should return false for nil arg")
+
+	// now set an error
+	err = errors.New("Some error")
+	False(t, ExactError(mockT, err, "Not some error"),
+		"ExactError should return false for different error string")
+	True(t, ExactError(mockT, err, "Some error"),
+		"ExactError should return true")
+}
+
 func Test_isEmpty(t *testing.T) {
 
 	True(t, isEmpty(""))

assert/errors.go

@@ -4,7 +4,7 @@ import (
 	"errors"
 )
 
-// AnError is an erorr instance useful for testing.  If the code does not care
+// AnError is an error instance useful for testing.  If the code does not care
 // about error specifics, and only needs to return the error for example, this
 // error should be used to make the test code more readable.
 var AnError error = errors.New("assert.AnError general error for testing.")