[Bug]: Difference in diffs between MatchSnapshot and MatchStandaloneSnapshot

[artuross]

Description

I have a very simple test case like this:

		requestBody := map[string]string{
			"email":    "test@example.com",
			"password": "password13",
		}
		body, err := json.Marshal(requestBody)
		require.NoError(t, err)

		req := httptest.NewRequest(http.MethodPost, "/sign-in", bytes.NewReader(body))
		req.Header.Set("Content-Type", "application/json")
		recorder := httptest.NewRecorder()

		requestDump, err := httputil.DumpRequest(req, true)
		require.NoError(t, err)
		snaps.MatchSnapshot(t, string(requestDump))
		snaps.MatchStandaloneSnapshot(t, string(requestDump))

The gist is that I create a new request and dump the request in standard text representation. That representation is saved as a snapshot. I've noticed that there's difference between how MatchSnapshot prints the diff vs how MatchStandaloneSnapshot does it.

Here's an example output (in both cases, this is the only snapshot available in a file):

--- FAIL: TestHandleSignIn (0.00s)
    --- FAIL: TestHandleSignIn/should_return_201_and_token_when_sign_in_succeeds (0.00s)
        auth_sign_in_test.go:42: 
            - Snapshot - 5
            + Received + 5
            
            - POST /sign-in HTTP/1.1
            - Host: example.com
            - Content-Type: application/json
            - 
            - {"email":"test@example.com","password":"password12"}
            + POST /sign-in HTTP/1.1
            + Host: example.com
            + Content-Type: application/json
            + 
            + {"email":"test@example.com","password":"password13"}
            
            at __snapshots__/auth_sign_in_test.snap:2
            
        auth_sign_in_test.go:43: 
            - Snapshot - 1
            + Received + 1
            
              Host: example.com
              Content-Type: application/json
              
            - {"email":"test@example.com","password":"password12"}
            + {"email":"test@example.com","password":"password13"}
            
            at __snapshots__/TestHandleSignIn_should_return_201_and_token_when_sign_in_succeeds_1.snap:1

As you can see the output from MatchStandaloneSnapshot is much better showing only the line that actually changed.

Steps to Reproduce

1. Prepare a test like this:

		requestBody := map[string]string{
			"email":    "test@example.com",
			"password": "password12",
		}
		body, err := json.Marshal(requestBody)
		require.NoError(t, err)

		req := httptest.NewRequest(http.MethodPost, "/sign-in", bytes.NewReader(body))
		req.Header.Set("Content-Type", "application/json")
		recorder := httptest.NewRecorder()

		requestDump, err := httputil.DumpRequest(req, true)
		require.NoError(t, err)
		snaps.MatchSnapshot(t, string(requestDump))
		snaps.MatchStandaloneSnapshot(t, string(requestDump))

2. go test ./...
3. Change requestBody (e.g. add a character to one of the values).
4. go test ./...

Expected Behavior

Both snapshots should only show the line that changed.

[gkampitakis]

Hey 👋 Thanks for opening this issue and sharing the detailed context. This is not a bug per se but a limitation of MatchSnapshot . The reason this is happening is because

snaps.MatchSnapshot(t, string(requestDump))

contains crlf characters that get dropped when reading the snapshot from the file.

if you change your code to this

snaps.MatchSnapshot(t, strings.ReplaceAll(string(requestDump), "\r\n", "\n"))

it works as expected if you need a workaround now.I might have a solution but it will need some further testing and validation to make sure it's not creating a regresion. Will create a draft pr to check if you are interested to test.

[artuross]

Hey @gkampitakis, thanks for such a quick answer. I recall I saw it mentioned somewhere that this library doesn't support \r\n, but tbh it probably would be good to still handle that.

Your workaround is good enough for me now. Thanks!

[G-Rath]

@gkampitakis hate to say it, but this has caused a regression for us - both osv-scanner and osv-detector are now failing their Windows snapshots as it cannot find the snaps, which doesn't happen with this reverted:

• fix(deps): update osv-detector minor G-Rath/osv-detector#344
  • https://github.com/G-Rath/osv-detector/actions/runs/19723084100/job/56509152040
• fix(deps): update osv-scanner minor google/osv-scanner#2365
• chore: use fork G-Rath/osv-detector#351

[gkampitakis]

ahhh dammit. Sorry reverting this asap. I have windows as target on go-snaps tests but didn't caught the regression.

[gkampitakis]

I did a wrong tag but 0.5.18 has the revert. Again sorry will have a look why I missed the windows :/

[G-Rath]

@gkampitakis it's because you're turning off autocrtl in your Windows tests - see #147