errors_test.go

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package fmt_test
     6  
     7  import (
     8  	"errors"
     9  	"fmt"
    10  	"reflect"
    11  	"testing"
    12  )
    13  
    14  func TestErrorf(t *testing.T) {
    15  	// noVetErrorf is an alias for fmt.Errorf that does not trigger vet warnings for
    16  	// %w format strings.
    17  	noVetErrorf := fmt.Errorf
    18  
    19  	wrapped := errors.New("inner error")
    20  	for _, test := range []struct {
    21  		err        error
    22  		wantText   string
    23  		wantUnwrap error
    24  		wantSplit  []error
    25  	}{{
    26  		err:        fmt.Errorf("%w", wrapped),
    27  		wantText:   "inner error",
    28  		wantUnwrap: wrapped,
    29  	}, {
    30  		err:        fmt.Errorf("added context: %w", wrapped),
    31  		wantText:   "added context: inner error",
    32  		wantUnwrap: wrapped,
    33  	}, {
    34  		err:        fmt.Errorf("%w with added context", wrapped),
    35  		wantText:   "inner error with added context",
    36  		wantUnwrap: wrapped,
    37  	}, {
    38  		err:        fmt.Errorf("%s %w %v", "prefix", wrapped, "suffix"),
    39  		wantText:   "prefix inner error suffix",
    40  		wantUnwrap: wrapped,
    41  	}, {
    42  		err:        fmt.Errorf("%[2]s: %[1]w", wrapped, "positional verb"),
    43  		wantText:   "positional verb: inner error",
    44  		wantUnwrap: wrapped,
    45  	}, {
    46  		err:      fmt.Errorf("%v", wrapped),
    47  		wantText: "inner error",
    48  	}, {
    49  		err:      fmt.Errorf("added context: %v", wrapped),
    50  		wantText: "added context: inner error",
    51  	}, {
    52  		err:      fmt.Errorf("%v with added context", wrapped),
    53  		wantText: "inner error with added context",
    54  	}, {
    55  		err:      noVetErrorf("%w is not an error", "not-an-error"),
    56  		wantText: "%!w(string=not-an-error) is not an error",
    57  	}, {
    58  		err:       noVetErrorf("wrapped two errors: %w %w", errString("1"), errString("2")),
    59  		wantText:  "wrapped two errors: 1 2",
    60  		wantSplit: []error{errString("1"), errString("2")},
    61  	}, {
    62  		err:       noVetErrorf("wrapped three errors: %w %w %w", errString("1"), errString("2"), errString("3")),
    63  		wantText:  "wrapped three errors: 1 2 3",
    64  		wantSplit: []error{errString("1"), errString("2"), errString("3")},
    65  	}, {
    66  		err:       noVetErrorf("wrapped nil error: %w %w %w", errString("1"), nil, errString("2")),
    67  		wantText:  "wrapped nil error: 1 %!w(<nil>) 2",
    68  		wantSplit: []error{errString("1"), errString("2")},
    69  	}, {
    70  		err:       noVetErrorf("wrapped one non-error: %w %w %w", errString("1"), "not-an-error", errString("3")),
    71  		wantText:  "wrapped one non-error: 1 %!w(string=not-an-error) 3",
    72  		wantSplit: []error{errString("1"), errString("3")},
    73  	}, {
    74  		err:       fmt.Errorf("wrapped errors out of order: %[3]w %[2]w %[1]w", errString("1"), errString("2"), errString("3")),
    75  		wantText:  "wrapped errors out of order: 3 2 1",
    76  		wantSplit: []error{errString("1"), errString("2"), errString("3")},
    77  	}, {
    78  		err:       fmt.Errorf("wrapped several times: %[1]w %[1]w %[2]w %[1]w", errString("1"), errString("2")),
    79  		wantText:  "wrapped several times: 1 1 2 1",
    80  		wantSplit: []error{errString("1"), errString("2")},
    81  	}, {
    82  		err:        fmt.Errorf("%w", nil),
    83  		wantText:   "%!w(<nil>)",
    84  		wantUnwrap: nil, // still nil
    85  	}} {
    86  		if got, want := errors.Unwrap(test.err), test.wantUnwrap; got != want {
    87  			t.Errorf("Formatted error: %v\nerrors.Unwrap() = %v, want %v", test.err, got, want)
    88  		}
    89  		if got, want := splitErr(test.err), test.wantSplit; !reflect.DeepEqual(got, want) {
    90  			t.Errorf("Formatted error: %v\nUnwrap() []error = %v, want %v", test.err, got, want)
    91  		}
    92  		if got, want := test.err.Error(), test.wantText; got != want {
    93  			t.Errorf("err.Error() = %q, want %q", got, want)
    94  		}
    95  	}
    96  }
    97  
    98  func splitErr(err error) []error {
    99  	if e, ok := err.(interface{ Unwrap() []error }); ok {
   100  		return e.Unwrap()
   101  	}
   102  	return nil
   103  }
   104  
   105  type errString string
   106  
   107  func (e errString) Error() string { return string(e) }
   108
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