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Create a simple example for the IgnoreFields #205

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merged 5 commits into from Oct 4, 2020
Merged

Create a simple example for the IgnoreFields #205

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86c02c9
Create a simple example for the IgnoreFields
colinnewell May 31, 2020
6f9a084
Fixed test issue with non deterministic output
colinnewell Oct 3, 2020
41bf780
Code review fixes
colinnewell Oct 4, 2020
cfdd12b
More code review tweaks.
colinnewell Oct 4, 2020
0ae3bec
Used better suggestion of wording from code review
colinnewell Oct 4, 2020
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125 changes: 125 additions & 0 deletions cmp/cmpopts/example_test.go
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package cmpopts_test
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Please add license header.

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Done

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I know people aren't fond of 2020, but that's the current year ;)


import (
"fmt"
"net"
"time"

"github.com/google/go-cmp/cmp"
"github.com/google/go-cmp/cmp/cmpopts"
"github.com/google/go-cmp/cmp/internal/flags"
)

func init() {
flags.Deterministic = true
}

// Use IgnoreFields to ignore fields on a type when comparing.
// Provide an interface of the type, and the field names to ignore.
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func ExampleIgnoreFields_testing() {
// Let got be the hypothetical value obtained from some logic under test
// and want be the expected golden data.
got, want := MakeGatewayInfo()

// Note that the Diff will still potentially show ignored fields as different,
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will still potentially show ignored fields as different,

Is still true? I recall fixing the reporter to stop printing ignored fields and using ... instead, even for adjacent fields.

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go-cmp/cmp/report_compare.go

Lines 258 to 265 in d713870

// Elide ignored nodes.
if r.Value.NumIgnored > 0 && r.Value.NumSame+r.Value.NumDiff == 0 {
deferredEllipsis = !(k == reflect.Slice || k == reflect.Array)
if !deferredEllipsis {
list.AppendEllipsis(diffStats{})
}
continue
}

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The example itself demonstrates what I was trying to say. I ignore IPAddress but it still shows up in the diff. I assume that the reason I added 'potentially' to the sentence is because I had come across your behaviour to minimise that.

If you do end up changing that behaviour, the example will highlight it so it should be easy to change that comment then.

Alternatively, is it the word 'adjacent' that you're objecting to?

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I think there's a crucial difference between "in the diff" as you just said versus "as different" as currently written in the example. The former denotes an issues with display representation, while the latter subtly suggests something about the semantics of how the comparison is performed.

Perhaps this is better worded as:

// While the specified fields will be semantically ignored for the comparison,
// the fields may be printed in the diff when displaying entire values
// that are already determined to be different.

// but only because they are adjacent to other fields that are also different.
if diff := cmp.Diff(want, got, cmpopts.IgnoreFields(Client{}, "IPAddress")); diff != "" {
t.Errorf("MakeGatewayInfo() mismatch (-want +got):\n%s", diff)
}

// Output:
// MakeGatewayInfo() mismatch (-want +got):
// cmpopts_test.Gateway{
// SSID: "CoffeeShopWiFi",
// - IPAddress: s"192.168.0.2",
// + IPAddress: s"192.168.0.1",
// NetMask: {0xff, 0xff, 0x00, 0x00},
// Clients: []cmpopts_test.Client{
// ... // 3 identical elements
// {Hostname: "espresso", ...},
// {Hostname: "latte", LastSeen: s"2009-11-10 23:00:23 +0000 UTC", ...},
// + {
// + Hostname: "americano",
// + IPAddress: s"192.168.0.188",
// + LastSeen: s"2009-11-10 23:03:05 +0000 UTC",
// + },
// },
// }

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}

type (
Gateway struct {
SSID string
IPAddress net.IP
NetMask net.IPMask
Clients []Client
}
Client struct {
Hostname string
IPAddress net.IP
LastSeen time.Time
}
)

func MakeGatewayInfo() (x, y Gateway) {
x = Gateway{
SSID: "CoffeeShopWiFi",
IPAddress: net.IPv4(192, 168, 0, 1),
NetMask: net.IPv4Mask(255, 255, 0, 0),
Clients: []Client{{
Hostname: "ristretto",
IPAddress: net.IPv4(192, 168, 0, 116),
}, {
Hostname: "aribica",
IPAddress: net.IPv4(192, 168, 0, 104),
LastSeen: time.Date(2009, time.November, 10, 23, 6, 32, 0, time.UTC),
}, {
Hostname: "macchiato",
IPAddress: net.IPv4(192, 168, 0, 153),
LastSeen: time.Date(2009, time.November, 10, 23, 39, 43, 0, time.UTC),
}, {
Hostname: "espresso",
IPAddress: net.IPv4(192, 168, 0, 121),
}, {
Hostname: "latte",
IPAddress: net.IPv4(192, 168, 0, 219),
LastSeen: time.Date(2009, time.November, 10, 23, 0, 23, 0, time.UTC),
}, {
Hostname: "americano",
IPAddress: net.IPv4(192, 168, 0, 188),
LastSeen: time.Date(2009, time.November, 10, 23, 3, 5, 0, time.UTC),
}},
}
y = Gateway{
SSID: "CoffeeShopWiFi",
IPAddress: net.IPv4(192, 168, 0, 2),
NetMask: net.IPv4Mask(255, 255, 0, 0),
Clients: []Client{{
Hostname: "ristretto",
IPAddress: net.IPv4(192, 168, 0, 116),
}, {
Hostname: "aribica",
IPAddress: net.IPv4(192, 168, 0, 104),
LastSeen: time.Date(2009, time.November, 10, 23, 6, 32, 0, time.UTC),
}, {
Hostname: "macchiato",
IPAddress: net.IPv4(192, 168, 0, 153),
LastSeen: time.Date(2009, time.November, 10, 23, 39, 43, 0, time.UTC),
}, {
Hostname: "espresso",
IPAddress: net.IPv4(192, 168, 0, 121),
}, {
Hostname: "latte",
IPAddress: net.IPv4(192, 168, 0, 221),
LastSeen: time.Date(2009, time.November, 10, 23, 0, 23, 0, time.UTC),
}},
}
return x, y
}

var t fakeT

type fakeT struct{}

func (t fakeT) Errorf(format string, args ...interface{}) { fmt.Printf(format+"\n", args...) }