refactor: static sentinel errors for #55's config validation paths (err113)

internal/config/cache_max_bytes_internal_test.go

@@ -9,6 +9,12 @@ import (
 	"testing"
 )
 
+// Static errors returned by the stub free-space probes below.
+var (
+	errTestStatfsFailed     = errors.New("statfs failed")
+	errTestProbeNotExpected = errors.New("probe must not be called")
+)
+
 // discardLogger returns a logger that swallows all output, for tests
 // that exercise code paths which log.
 func discardLogger() *slog.Logger {
@@ -205,7 +211,7 @@ func TestComputeDefaultCacheMaxBytesAppliesFloorToComputedDefault(t *testing.T)
 func TestComputeDefaultCacheMaxBytesPropagatesProbeError(t *testing.T) {
 	t.Parallel()
 
-	probe := func(string) (uint64, error) { return 0, errors.New("statfs failed") }
+	probe := func(string) (uint64, error) { return 0, errTestStatfsFailed }
 
 	_, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
 	if err == nil {
@@ -284,7 +290,7 @@ func TestResolveCacheMaxBytesDoesNotOverrideExplicitValue(t *testing.T) {
 	probe := func(string) (uint64, error) {
 		t.Error("free-space probe must not be consulted for explicit values")
 
-		return 0, errors.New("probe must not be called")
+		return 0, errTestProbeNotExpected
 	}
 
 	err = c.resolveCacheMaxBytes(discardLogger(), probe)