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:      fmt.Errorf("no verbs"),
    59  		wantText: "no verbs",
    60  	}, {
    61  		err:      noVetErrorf("no verbs with extra arg", "extra"),
    62  		wantText: "no verbs with extra arg%!(EXTRA string=extra)",
    63  	}, {
    64  		err:      noVetErrorf("too many verbs: %w %v"),
    65  		wantText: "too many verbs: %!w(MISSING) %!v(MISSING)",
    66  	}, {
    67  		err:       noVetErrorf("wrapped two errors: %w %w", errString("1"), errString("2")),
    68  		wantText:  "wrapped two errors: 1 2",
    69  		wantSplit: []error{errString("1"), errString("2")},
    70  	}, {
    71  		err:       noVetErrorf("wrapped three errors: %w %w %w", errString("1"), errString("2"), errString("3")),
    72  		wantText:  "wrapped three errors: 1 2 3",
    73  		wantSplit: []error{errString("1"), errString("2"), errString("3")},
    74  	}, {
    75  		err:       noVetErrorf("wrapped nil error: %w %w %w", errString("1"), nil, errString("2")),
    76  		wantText:  "wrapped nil error: 1 %!w(<nil>) 2",
    77  		wantSplit: []error{errString("1"), errString("2")},
    78  	}, {
    79  		err:       noVetErrorf("wrapped one non-error: %w %w %w", errString("1"), "not-an-error", errString("3")),
    80  		wantText:  "wrapped one non-error: 1 %!w(string=not-an-error) 3",
    81  		wantSplit: []error{errString("1"), errString("3")},
    82  	}, {
    83  		err:       fmt.Errorf("wrapped errors out of order: %[3]w %[2]w %[1]w", errString("1"), errString("2"), errString("3")),
    84  		wantText:  "wrapped errors out of order: 3 2 1",
    85  		wantSplit: []error{errString("1"), errString("2"), errString("3")},
    86  	}, {
    87  		err:       fmt.Errorf("wrapped several times: %[1]w %[1]w %[2]w %[1]w", errString("1"), errString("2")),
    88  		wantText:  "wrapped several times: 1 1 2 1",
    89  		wantSplit: []error{errString("1"), errString("2")},
    90  	}, {
    91  		err:        fmt.Errorf("%w", nil),
    92  		wantText:   "%!w(<nil>)",
    93  		wantUnwrap: nil, // still nil
    94  	}} {
    95  		if got, want := errors.Unwrap(test.err), test.wantUnwrap; got != want {
    96  			t.Errorf("Formatted error: %v\nerrors.Unwrap() = %v, want %v", test.err, got, want)
    97  		}
    98  		if got, want := splitErr(test.err), test.wantSplit; !reflect.DeepEqual(got, want) {
    99  			t.Errorf("Formatted error: %v\nUnwrap() []error = %v, want %v", test.err, got, want)
   100  		}
   101  		if got, want := test.err.Error(), test.wantText; got != want {
   102  			t.Errorf("err.Error() = %q, want %q", got, want)
   103  		}
   104  	}
   105  }
   106  
   107  func splitErr(err error) []error {
   108  	if e, ok := err.(interface{ Unwrap() []error }); ok {
   109  		return e.Unwrap()
   110  	}
   111  	return nil
   112  }
   113  
   114  type errString string
   115  
   116  func (e errString) Error() string { return string(e) }
   117
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