testutil: new TempFile function, simplify WriteToNewTempFile (#8123)

Files returned by WriteToNewTempFile are cleaned up
automatically at the end of a test case execution.
WriteToNewTempFile now relies on the TB.TempDir()
function provided by the testing std package.

TempFile returns a temporary file that can be used
within a test case and is automatically removed
at the end of the test execution.

testutil/ioutil.go

@@ -52,15 +52,22 @@ func ApplyMockIODiscardOutErr(c *cobra.Command) BufferReader {
 }
 
 // Write the given string to a new temporary file.
-// Returns an open file and a clean up function that
-// the caller must call to remove the file when it is
-// no longer needed.
-func WriteToNewTempFile(t testing.TB, s string) (*os.File, func()) {
-	fp, err := ioutil.TempFile("", strings.ReplaceAll(t.Name(), "/", "_")+"_")
+// Returns an open file for the test to use.
+func WriteToNewTempFile(t testing.TB, s string) *os.File {
+	t.Helper()
+
+	fp, err := TempFile(t)
 	require.Nil(t, err)
 
 	_, err = fp.WriteString(s)
 	require.Nil(t, err)
 
-	return fp, func() { os.Remove(fp.Name()) }
+	return fp
+}
+
+// TempFile returns a writable temporary file for the test to use.
+func TempFile(t testing.TB) (*os.File, error) {
+	t.Helper()
+
+	return ioutil.TempFile(t.TempDir(), "")
 }

testutil/ioutil_test.go

@@ -25,16 +25,12 @@ func TestApplyMockIO(t *testing.T) {
 }
 
 func TestWriteToNewTempFile(t *testing.T) {
-	tempfile, cleanup := testutil.WriteToNewTempFile(t, "test string")
+	tempfile := testutil.WriteToNewTempFile(t, "test string")
 	tempfile.Close()
 
 	bs, err := ioutil.ReadFile(tempfile.Name())
 	require.NoError(t, err)
 	require.Equal(t, "test string", string(bs))
-
-	cleanup()
-
-	require.NoFileExists(t, tempfile.Name())
 }
 
 func TestApplyMockIODiscardOutErr(t *testing.T) {