tusd: `TestWriteChunkCleansUpTempFiles` test fails at random times

The S3 test TestWriteChunkCleansUpTempFiles fails at random times, especially in the CI pipeline, and only seems to be on linux.

Doing some digging locally, and I see that the temp directory has three files in it when the test fails. 1 at 10 bytes with 1234567890 1 at 4 bytes with ABCD 1 at 0 bytes (this is the one that causes the test to fail)

--- FAIL: TestWriteChunkCleansUpTempFiles (0.00s)
    s3store_test.go:1278: 
        	Error Trace:	s3store_test.go:1278
        	            				s3store.go:414
        	            				s3store.go:382
        	            				s3store_test.go:1350
        	Error:      	Not equal: 
        	            	expected: 3
        	            	actual  : 2
        	Test:       	TestWriteChunkCleansUpTempFiles

Using this dockerfile

FROM golang:1.17.2
WORKDIR /go/src/github.com/tus/tusd
COPY go.mod go.sum ./
RUN go mod download
COPY cmd ./cmd/
COPY internal ./internal/
COPY pkg ./pkg/

CMD [ "go", "test", "./pkg/s3store", "-v" ]

With this patch on the S3 test

diff --git a/pkg/s3store/s3store_test.go b/pkg/s3store/s3store_test.go
index 88ec09a..a5ec33f 100644
--- a/pkg/s3store/s3store_test.go
+++ b/pkg/s3store/s3store_test.go
@@ -5,6 +5,7 @@ import (
        "context"
        "fmt"
        "io/ioutil"
+       "path/filepath"
        "strings"
        "testing"
        "time"
@@ -1273,6 +1274,9 @@ func (s s3APIWithTempFileAssertion) UploadPartWithContext(context.Context, *s3.U
        files, err := ioutil.ReadDir(s.tempDir)
        assert.Nil(err)
        for _, file := range files {
+               // Print the file name and file size to make it easier to find the file.
+               content, _ := ioutil.ReadFile(filepath.Join(s.tempDir, file.Name()))
+               fmt.Printf("%s (%d bytes): %s\n", file.Name(), file.Size(), string(content))
                assert.True(strings.HasPrefix(file.Name(), "tusd-s3-tmp-"))
        }
        assert.Equal(len(files), 2)

It shows the file, its size and contents. When it fails, it’ll show a third file with 0 bytes in it.