vendor/github.com/go-check/check/checkers.go - third_party/github.com/moby/moby - Git at Google

 package check

 import (
 	"fmt"
 	"reflect"
 	"regexp"
 )

 // -----------------------------------------------------------------------
 // CommentInterface and Commentf helper, to attach extra information to checks.

 type comment struct {
 	format string
 	args   []interface{}
 }

 // Commentf returns an infomational value to use with Assert or Check calls.
 // If the checker test fails, the provided arguments will be passed to
 // fmt.Sprintf, and will be presented next to the logged failure.
 //
 // For example:
 //
 //     c.Assert(v, Equals, 42, Commentf("Iteration #%d failed.", i))
 //
 // Note that if the comment is constant, a better option is to
 // simply use a normal comment right above or next to the line, as
 // it will also get printed with any errors:
 //
 //     c.Assert(l, Equals, 8192) // Ensure buffer size is correct (bug #123)
 //
 func Commentf(format string, args ...interface{}) CommentInterface {
 	return &comment{format, args}
 }

 // CommentInterface must be implemented by types that attach extra
 // information to failed checks. See the Commentf function for details.
 type CommentInterface interface {
 	CheckCommentString() string
 }

 func (c *comment) CheckCommentString() string {
 	return fmt.Sprintf(c.format, c.args...)
 }

 // -----------------------------------------------------------------------
 // The Checker interface.

 // The Checker interface must be provided by checkers used with
 // the Assert and Check verification methods.
 type Checker interface {
 	Info() *CheckerInfo
 	Check(params []interface{}, names []string) (result bool, error string)
 }

 // See the Checker interface.
 type CheckerInfo struct {
 	Name   string
 	Params []string
 }

 func (info *CheckerInfo) Info() *CheckerInfo {
 	return info
 }

 // -----------------------------------------------------------------------
 // Not checker logic inverter.

 // The Not checker inverts the logic of the provided checker.  The
 // resulting checker will succeed where the original one failed, and
 // vice-versa.
 //
 // For example:
 //
 //     c.Assert(a, Not(Equals), b)
 //
 func Not(checker Checker) Checker {
 	return &notChecker{checker}
 }

 type notChecker struct {
 	sub Checker
 }

 func (checker *notChecker) Info() *CheckerInfo {
 	info := *checker.sub.Info()
 	info.Name = "Not(" + info.Name + ")"
 	return &info
 }

 func (checker *notChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	result, error = checker.sub.Check(params, names)
 	result = !result
 	return
 }

 // -----------------------------------------------------------------------
 // IsNil checker.

 type isNilChecker struct {
 	*CheckerInfo
 }

 // The IsNil checker tests whether the obtained value is nil.
 //
 // For example:
 //
 //    c.Assert(err, IsNil)
 //
 var IsNil Checker = &isNilChecker{
 	&CheckerInfo{Name: "IsNil", Params: []string{"value"}},
 }

 func (checker *isNilChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	return isNil(params[0]), ""
 }

 func isNil(obtained interface{}) (result bool) {
 	if obtained == nil {
 		result = true
 	} else {
 		switch v := reflect.ValueOf(obtained); v.Kind() {
 		case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
 			return v.IsNil()
 		}
 	}
 	return
 }

 // -----------------------------------------------------------------------
 // NotNil checker. Alias for Not(IsNil), since it's so common.

 type notNilChecker struct {
 	*CheckerInfo
 }

 // The NotNil checker verifies that the obtained value is not nil.
 //
 // For example:
 //
 //     c.Assert(iface, NotNil)
 //
 // This is an alias for Not(IsNil), made available since it's a
 // fairly common check.
 //
 var NotNil Checker = &notNilChecker{
 	&CheckerInfo{Name: "NotNil", Params: []string{"value"}},
 }

 func (checker *notNilChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	return !isNil(params[0]), ""
 }

 // -----------------------------------------------------------------------
 // Equals checker.

 type equalsChecker struct {
 	*CheckerInfo
 }

 // The Equals checker verifies that the obtained value is equal to
 // the expected value, according to usual Go semantics for ==.
 //
 // For example:
 //
 //     c.Assert(value, Equals, 42)
 //
 var Equals Checker = &equalsChecker{
 	&CheckerInfo{Name: "Equals", Params: []string{"obtained", "expected"}},
 }

 func (checker *equalsChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	defer func() {
 		if v := recover(); v != nil {
 			result = false
 			error = fmt.Sprint(v)
 		}
 	}()
 	return params[0] == params[1], ""
 }

 // -----------------------------------------------------------------------
 // DeepEquals checker.

 type deepEqualsChecker struct {
 	*CheckerInfo
 }

 // The DeepEquals checker verifies that the obtained value is deep-equal to
 // the expected value.  The check will work correctly even when facing
 // slices, interfaces, and values of different types (which always fail
 // the test).
 //
 // For example:
 //
 //     c.Assert(value, DeepEquals, 42)
 //     c.Assert(array, DeepEquals, []string{"hi", "there"})
 //
 var DeepEquals Checker = &deepEqualsChecker{
 	&CheckerInfo{Name: "DeepEquals", Params: []string{"obtained", "expected"}},
 }

 func (checker *deepEqualsChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	return reflect.DeepEqual(params[0], params[1]), ""
 }

 // -----------------------------------------------------------------------
 // HasLen checker.

 type hasLenChecker struct {
 	*CheckerInfo
 }

 // The HasLen checker verifies that the obtained value has the
 // provided length. In many cases this is superior to using Equals
 // in conjuction with the len function because in case the check
 // fails the value itself will be printed, instead of its length,
 // providing more details for figuring the problem.
 //
 // For example:
 //
 //     c.Assert(list, HasLen, 5)
 //
 var HasLen Checker = &hasLenChecker{
 	&CheckerInfo{Name: "HasLen", Params: []string{"obtained", "n"}},
 }

 func (checker *hasLenChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	n, ok := params[1].(int)
 	if !ok {
 		return false, "n must be an int"
 	}
 	value := reflect.ValueOf(params[0])
 	switch value.Kind() {
 	case reflect.Map, reflect.Array, reflect.Slice, reflect.Chan, reflect.String:
 	default:
 		return false, "obtained value type has no length"
 	}
 	return value.Len() == n, ""
 }

 // -----------------------------------------------------------------------
 // ErrorMatches checker.

 type errorMatchesChecker struct {
 	*CheckerInfo
 }

 // The ErrorMatches checker verifies that the error value
 // is non nil and matches the regular expression provided.
 //
 // For example:
 //
 //     c.Assert(err, ErrorMatches, "perm.*denied")
 //
 var ErrorMatches Checker = errorMatchesChecker{
 	&CheckerInfo{Name: "ErrorMatches", Params: []string{"value", "regex"}},
 }

 func (checker errorMatchesChecker) Check(params []interface{}, names []string) (result bool, errStr string) {
 	if params[0] == nil {
 		return false, "Error value is nil"
 	}
 	err, ok := params[0].(error)
 	if !ok {
 		return false, "Value is not an error"
 	}
 	params[0] = err.Error()
 	names[0] = "error"
 	return matches(params[0], params[1])
 }

 // -----------------------------------------------------------------------
 // Matches checker.

 type matchesChecker struct {
 	*CheckerInfo
 }

 // The Matches checker verifies that the string provided as the obtained
 // value (or the string resulting from obtained.String()) matches the
 // regular expression provided.
 //
 // For example:
 //
 //     c.Assert(err, Matches, "perm.*denied")
 //
 var Matches Checker = &matchesChecker{
 	&CheckerInfo{Name: "Matches", Params: []string{"value", "regex"}},
 }

 func (checker *matchesChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	return matches(params[0], params[1])
 }

 func matches(value, regex interface{}) (result bool, error string) {
 	reStr, ok := regex.(string)
 	if !ok {
 		return false, "Regex must be a string"
 	}
 	valueStr, valueIsStr := value.(string)
 	if !valueIsStr {
 		if valueWithStr, valueHasStr := value.(fmt.Stringer); valueHasStr {
 			valueStr, valueIsStr = valueWithStr.String(), true
 		}
 	}
 	if valueIsStr {
 		matches, err := regexp.MatchString("^"+reStr+"$", valueStr)
 		if err != nil {
 			return false, "Can't compile regex: " + err.Error()
 		}
 		return matches, ""
 	}
 	return false, "Obtained value is not a string and has no .String()"
 }

 // -----------------------------------------------------------------------
 // Panics checker.

 type panicsChecker struct {
 	*CheckerInfo
 }

 // The Panics checker verifies that calling the provided zero-argument
 // function will cause a panic which is deep-equal to the provided value.
 //
 // For example:
 //
 //     c.Assert(func() { f(1, 2) }, Panics, &SomeErrorType{"BOOM"}).
 //
 //
 var Panics Checker = &panicsChecker{
 	&CheckerInfo{Name: "Panics", Params: []string{"function", "expected"}},
 }

 func (checker *panicsChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	f := reflect.ValueOf(params[0])
 	if f.Kind() != reflect.Func || f.Type().NumIn() != 0 {
 		return false, "Function must take zero arguments"
 	}
 	defer func() {
 		// If the function has not panicked, then don't do the check.
 		if error != "" {
 			return
 		}
 		params[0] = recover()
 		names[0] = "panic"
 		result = reflect.DeepEqual(params[0], params[1])
 	}()
 	f.Call(nil)
 	return false, "Function has not panicked"
 }

 type panicMatchesChecker struct {
 	*CheckerInfo
 }

 // The PanicMatches checker verifies that calling the provided zero-argument
 // function will cause a panic with an error value matching
 // the regular expression provided.
 //
 // For example:
 //
 //     c.Assert(func() { f(1, 2) }, PanicMatches, `open.*: no such file or directory`).
 //
 //
 var PanicMatches Checker = &panicMatchesChecker{
 	&CheckerInfo{Name: "PanicMatches", Params: []string{"function", "expected"}},
 }

 func (checker *panicMatchesChecker) Check(params []interface{}, names []string) (result bool, errmsg string) {
 	f := reflect.ValueOf(params[0])
 	if f.Kind() != reflect.Func || f.Type().NumIn() != 0 {
 		return false, "Function must take zero arguments"
 	}
 	defer func() {
 		// If the function has not panicked, then don't do the check.
 		if errmsg != "" {
 			return
 		}
 		obtained := recover()
 		names[0] = "panic"
 		if e, ok := obtained.(error); ok {
 			params[0] = e.Error()
 		} else if _, ok := obtained.(string); ok {
 			params[0] = obtained
 		} else {
 			errmsg = "Panic value is not a string or an error"
 			return
 		}
 		result, errmsg = matches(params[0], params[1])
 	}()
 	f.Call(nil)
 	return false, "Function has not panicked"
 }

 // -----------------------------------------------------------------------
 // FitsTypeOf checker.

 type fitsTypeChecker struct {
 	*CheckerInfo
 }

 // The FitsTypeOf checker verifies that the obtained value is
 // assignable to a variable with the same type as the provided
 // sample value.
 //
 // For example:
 //
 //     c.Assert(value, FitsTypeOf, int64(0))
 //     c.Assert(value, FitsTypeOf, os.Error(nil))
 //
 var FitsTypeOf Checker = &fitsTypeChecker{
 	&CheckerInfo{Name: "FitsTypeOf", Params: []string{"obtained", "sample"}},
 }

 func (checker *fitsTypeChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	obtained := reflect.ValueOf(params[0])
 	sample := reflect.ValueOf(params[1])
 	if !obtained.IsValid() {
 		return false, ""
 	}
 	if !sample.IsValid() {
 		return false, "Invalid sample value"
 	}
 	return obtained.Type().AssignableTo(sample.Type()), ""
 }

 // -----------------------------------------------------------------------
 // Implements checker.

 type implementsChecker struct {
 	*CheckerInfo
 }

 // The Implements checker verifies that the obtained value
 // implements the interface specified via a pointer to an interface
 // variable.
 //
 // For example:
 //
 //     var e os.Error
 //     c.Assert(err, Implements, &e)
 //
 var Implements Checker = &implementsChecker{
 	&CheckerInfo{Name: "Implements", Params: []string{"obtained", "ifaceptr"}},
 }

 func (checker *implementsChecker) Check(params []interface{}, names []string) (result bool, error string) {
 	obtained := reflect.ValueOf(params[0])
 	ifaceptr := reflect.ValueOf(params[1])
 	if !obtained.IsValid() {
 		return false, ""
 	}
 	if !ifaceptr.IsValid() || ifaceptr.Kind() != reflect.Ptr || ifaceptr.Elem().Kind() != reflect.Interface {
 		return false, "ifaceptr should be a pointer to an interface variable"
 	}
 	return obtained.Type().Implements(ifaceptr.Elem().Type()), ""
 }
	package check

	import (
	"fmt"
	"reflect"
	"regexp"
	)

	// -----------------------------------------------------------------------
	// CommentInterface and Commentf helper, to attach extra information to checks.

	type comment struct {
	format string
	args []interface{}
	}

	// Commentf returns an infomational value to use with Assert or Check calls.
	// If the checker test fails, the provided arguments will be passed to
	// fmt.Sprintf, and will be presented next to the logged failure.
	//
	// For example:
	//
	// c.Assert(v, Equals, 42, Commentf("Iteration #%d failed.", i))
	//
	// Note that if the comment is constant, a better option is to
	// simply use a normal comment right above or next to the line, as
	// it will also get printed with any errors:
	//
	// c.Assert(l, Equals, 8192) // Ensure buffer size is correct (bug #123)
	//
	func Commentf(format string, args ...interface{}) CommentInterface {
	return &comment{format, args}
	}

	// CommentInterface must be implemented by types that attach extra
	// information to failed checks. See the Commentf function for details.
	type CommentInterface interface {
	CheckCommentString() string
	}

	func (c *comment) CheckCommentString() string {
	return fmt.Sprintf(c.format, c.args...)
	}

	// -----------------------------------------------------------------------
	// The Checker interface.

	// The Checker interface must be provided by checkers used with
	// the Assert and Check verification methods.
	type Checker interface {
	Info() *CheckerInfo
	Check(params []interface{}, names []string) (result bool, error string)
	}

	// See the Checker interface.
	type CheckerInfo struct {
	Name string
	Params []string
	}

	func (info CheckerInfo) Info() CheckerInfo {
	return info
	}

	// -----------------------------------------------------------------------
	// Not checker logic inverter.

	// The Not checker inverts the logic of the provided checker. The
	// resulting checker will succeed where the original one failed, and
	// vice-versa.
	//
	// For example:
	//
	// c.Assert(a, Not(Equals), b)
	//
	func Not(checker Checker) Checker {
	return &notChecker{checker}
	}

	type notChecker struct {
	sub Checker
	}

	func (checker notChecker) Info() CheckerInfo {
	info := *checker.sub.Info()
	info.Name = "Not(" + info.Name + ")"
	return &info
	}

	func (checker *notChecker) Check(params []interface{}, names []string) (result bool, error string) {
	result, error = checker.sub.Check(params, names)
	result = !result
	return
	}

	// -----------------------------------------------------------------------
	// IsNil checker.

	type isNilChecker struct {
	*CheckerInfo
	}

	// The IsNil checker tests whether the obtained value is nil.
	//
	// For example:
	//
	// c.Assert(err, IsNil)
	//
	var IsNil Checker = &isNilChecker{
	&CheckerInfo{Name: "IsNil", Params: []string{"value"}},
	}

	func (checker *isNilChecker) Check(params []interface{}, names []string) (result bool, error string) {
	return isNil(params[0]), ""
	}

	func isNil(obtained interface{}) (result bool) {
	if obtained == nil {
	result = true
	} else {
	switch v := reflect.ValueOf(obtained); v.Kind() {
	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
	return v.IsNil()
	}
	}
	return
	}

	// -----------------------------------------------------------------------
	// NotNil checker. Alias for Not(IsNil), since it's so common.

	type notNilChecker struct {
	*CheckerInfo
	}

	// The NotNil checker verifies that the obtained value is not nil.
	//
	// For example:
	//
	// c.Assert(iface, NotNil)
	//
	// This is an alias for Not(IsNil), made available since it's a
	// fairly common check.
	//
	var NotNil Checker = &notNilChecker{
	&CheckerInfo{Name: "NotNil", Params: []string{"value"}},
	}

	func (checker *notNilChecker) Check(params []interface{}, names []string) (result bool, error string) {
	return !isNil(params[0]), ""
	}

	// -----------------------------------------------------------------------
	// Equals checker.

	type equalsChecker struct {
	*CheckerInfo
	}

	// The Equals checker verifies that the obtained value is equal to
	// the expected value, according to usual Go semantics for ==.
	//
	// For example:
	//
	// c.Assert(value, Equals, 42)
	//
	var Equals Checker = &equalsChecker{
	&CheckerInfo{Name: "Equals", Params: []string{"obtained", "expected"}},
	}

	func (checker *equalsChecker) Check(params []interface{}, names []string) (result bool, error string) {
	defer func() {
	if v := recover(); v != nil {
	result = false
	error = fmt.Sprint(v)
	}
	}()
	return params[0] == params[1], ""
	}

	// -----------------------------------------------------------------------
	// DeepEquals checker.

	type deepEqualsChecker struct {
	*CheckerInfo
	}

	// The DeepEquals checker verifies that the obtained value is deep-equal to
	// the expected value. The check will work correctly even when facing
	// slices, interfaces, and values of different types (which always fail
	// the test).
	//
	// For example:
	//
	// c.Assert(value, DeepEquals, 42)
	// c.Assert(array, DeepEquals, []string{"hi", "there"})
	//
	var DeepEquals Checker = &deepEqualsChecker{
	&CheckerInfo{Name: "DeepEquals", Params: []string{"obtained", "expected"}},
	}

	func (checker *deepEqualsChecker) Check(params []interface{}, names []string) (result bool, error string) {
	return reflect.DeepEqual(params[0], params[1]), ""
	}

	// -----------------------------------------------------------------------
	// HasLen checker.

	type hasLenChecker struct {
	*CheckerInfo
	}

	// The HasLen checker verifies that the obtained value has the
	// provided length. In many cases this is superior to using Equals
	// in conjuction with the len function because in case the check
	// fails the value itself will be printed, instead of its length,
	// providing more details for figuring the problem.
	//
	// For example:
	//
	// c.Assert(list, HasLen, 5)
	//
	var HasLen Checker = &hasLenChecker{
	&CheckerInfo{Name: "HasLen", Params: []string{"obtained", "n"}},
	}

	func (checker *hasLenChecker) Check(params []interface{}, names []string) (result bool, error string) {
	n, ok := params[1].(int)
	if !ok {
	return false, "n must be an int"
	}
	value := reflect.ValueOf(params[0])
	switch value.Kind() {
	case reflect.Map, reflect.Array, reflect.Slice, reflect.Chan, reflect.String:
	default:
	return false, "obtained value type has no length"
	}
	return value.Len() == n, ""
	}

	// -----------------------------------------------------------------------
	// ErrorMatches checker.

	type errorMatchesChecker struct {
	*CheckerInfo
	}

	// The ErrorMatches checker verifies that the error value
	// is non nil and matches the regular expression provided.
	//
	// For example:
	//
	// c.Assert(err, ErrorMatches, "perm.*denied")
	//
	var ErrorMatches Checker = errorMatchesChecker{
	&CheckerInfo{Name: "ErrorMatches", Params: []string{"value", "regex"}},
	}

	func (checker errorMatchesChecker) Check(params []interface{}, names []string) (result bool, errStr string) {
	if params[0] == nil {
	return false, "Error value is nil"
	}
	err, ok := params[0].(error)
	if !ok {
	return false, "Value is not an error"
	}
	params[0] = err.Error()
	names[0] = "error"
	return matches(params[0], params[1])
	}

	// -----------------------------------------------------------------------
	// Matches checker.

	type matchesChecker struct {
	*CheckerInfo
	}

	// The Matches checker verifies that the string provided as the obtained
	// value (or the string resulting from obtained.String()) matches the
	// regular expression provided.
	//
	// For example:
	//
	// c.Assert(err, Matches, "perm.*denied")
	//
	var Matches Checker = &matchesChecker{
	&CheckerInfo{Name: "Matches", Params: []string{"value", "regex"}},
	}

	func (checker *matchesChecker) Check(params []interface{}, names []string) (result bool, error string) {
	return matches(params[0], params[1])
	}

	func matches(value, regex interface{}) (result bool, error string) {
	reStr, ok := regex.(string)
	if !ok {
	return false, "Regex must be a string"
	}
	valueStr, valueIsStr := value.(string)
	if !valueIsStr {
	if valueWithStr, valueHasStr := value.(fmt.Stringer); valueHasStr {
	valueStr, valueIsStr = valueWithStr.String(), true
	}
	}
	if valueIsStr {
	matches, err := regexp.MatchString("^"+reStr+"$", valueStr)
	if err != nil {
	return false, "Can't compile regex: " + err.Error()
	}
	return matches, ""
	}
	return false, "Obtained value is not a string and has no .String()"
	}

	// -----------------------------------------------------------------------
	// Panics checker.

	type panicsChecker struct {
	*CheckerInfo
	}

	// The Panics checker verifies that calling the provided zero-argument
	// function will cause a panic which is deep-equal to the provided value.
	//
	// For example:
	//
	// c.Assert(func() { f(1, 2) }, Panics, &SomeErrorType{"BOOM"}).
	//
	//
	var Panics Checker = &panicsChecker{
	&CheckerInfo{Name: "Panics", Params: []string{"function", "expected"}},
	}

	func (checker *panicsChecker) Check(params []interface{}, names []string) (result bool, error string) {
	f := reflect.ValueOf(params[0])
	if f.Kind() != reflect.Func \|\| f.Type().NumIn() != 0 {
	return false, "Function must take zero arguments"
	}
	defer func() {
	// If the function has not panicked, then don't do the check.
	if error != "" {
	return
	}
	params[0] = recover()
	names[0] = "panic"
	result = reflect.DeepEqual(params[0], params[1])
	}()
	f.Call(nil)
	return false, "Function has not panicked"
	}

	type panicMatchesChecker struct {
	*CheckerInfo
	}

	// The PanicMatches checker verifies that calling the provided zero-argument
	// function will cause a panic with an error value matching
	// the regular expression provided.
	//
	// For example:
	//
	// c.Assert(func() { f(1, 2) }, PanicMatches, `open.*: no such file or directory`).
	//
	//
	var PanicMatches Checker = &panicMatchesChecker{
	&CheckerInfo{Name: "PanicMatches", Params: []string{"function", "expected"}},
	}

	func (checker *panicMatchesChecker) Check(params []interface{}, names []string) (result bool, errmsg string) {
	f := reflect.ValueOf(params[0])
	if f.Kind() != reflect.Func \|\| f.Type().NumIn() != 0 {
	return false, "Function must take zero arguments"
	}
	defer func() {
	// If the function has not panicked, then don't do the check.
	if errmsg != "" {
	return
	}
	obtained := recover()
	names[0] = "panic"
	if e, ok := obtained.(error); ok {
	params[0] = e.Error()
	} else if _, ok := obtained.(string); ok {
	params[0] = obtained
	} else {
	errmsg = "Panic value is not a string or an error"
	return
	}
	result, errmsg = matches(params[0], params[1])
	}()
	f.Call(nil)
	return false, "Function has not panicked"
	}

	// -----------------------------------------------------------------------
	// FitsTypeOf checker.

	type fitsTypeChecker struct {
	*CheckerInfo
	}

	// The FitsTypeOf checker verifies that the obtained value is
	// assignable to a variable with the same type as the provided
	// sample value.
	//
	// For example:
	//
	// c.Assert(value, FitsTypeOf, int64(0))
	// c.Assert(value, FitsTypeOf, os.Error(nil))
	//
	var FitsTypeOf Checker = &fitsTypeChecker{
	&CheckerInfo{Name: "FitsTypeOf", Params: []string{"obtained", "sample"}},
	}

	func (checker *fitsTypeChecker) Check(params []interface{}, names []string) (result bool, error string) {
	obtained := reflect.ValueOf(params[0])
	sample := reflect.ValueOf(params[1])
	if !obtained.IsValid() {
	return false, ""
	}
	if !sample.IsValid() {
	return false, "Invalid sample value"
	}
	return obtained.Type().AssignableTo(sample.Type()), ""
	}

	// -----------------------------------------------------------------------
	// Implements checker.

	type implementsChecker struct {
	*CheckerInfo
	}

	// The Implements checker verifies that the obtained value
	// implements the interface specified via a pointer to an interface
	// variable.
	//
	// For example:
	//
	// var e os.Error
	// c.Assert(err, Implements, &e)
	//
	var Implements Checker = &implementsChecker{
	&CheckerInfo{Name: "Implements", Params: []string{"obtained", "ifaceptr"}},
	}

	func (checker *implementsChecker) Check(params []interface{}, names []string) (result bool, error string) {
	obtained := reflect.ValueOf(params[0])
	ifaceptr := reflect.ValueOf(params[1])
	if !obtained.IsValid() {
	return false, ""
	}
	if !ifaceptr.IsValid() \|\| ifaceptr.Kind() != reflect.Ptr \|\| ifaceptr.Elem().Kind() != reflect.Interface {
	return false, "ifaceptr should be a pointer to an interface variable"
	}
	return obtained.Type().Implements(ifaceptr.Elem().Type()), ""
	}