1 files changed, 99 insertions, 0 deletions
diff --git a/lib/util/fmt_test.go b/lib/util/fmt_test.go
new file mode 100644
index 0000000..4251ecf
--- /dev/null
+++ b/lib/util/fmt_test.go
@@ -0,0 +1,99 @@
+package util_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"git.lukeshu.com/btrfs-progs-ng/lib/util"
+)
+
+type FmtState struct {
+	MWidth     int
+	MPrec      int
+	MFlagMinus bool
+	MFlagPlus  bool
+	MFlagSharp bool
+	MFlagSpace bool
+	MFlagZero  bool
+}
+
+func (st FmtState) Width() (int, bool) {
+	if st.MWidth < 1 {
+		return 0, false
+	}
+	return st.MWidth, true
+}
+
+func (st FmtState) Precision() (int, bool) {
+	if st.MPrec < 1 {
+		return 0, false
+	}
+	return st.MPrec, true
+}
+
+func (st FmtState) Flag(b int) bool {
+	switch b {
+	case '-':
+		return st.MFlagMinus
+	case '+':
+		return st.MFlagPlus
+	case '#':
+		return st.MFlagSharp
+	case ' ':
+		return st.MFlagSpace
+	case '0':
+		return st.MFlagZero
+	}
+	return false
+}
+
+func (st FmtState) Write([]byte) (int, error) {
+	panic("not implemented")
+}
+
+func (dst *FmtState) Format(src fmt.State, verb rune) {
+	if width, ok := src.Width(); ok {
+		dst.MWidth = width
+	}
+	if prec, ok := src.Precision(); ok {
+		dst.MPrec = prec
+	}
+	dst.MFlagMinus = src.Flag('-')
+	dst.MFlagPlus = src.Flag('+')
+	dst.MFlagSharp = src.Flag('#')
+	dst.MFlagSpace = src.Flag(' ')
+	dst.MFlagZero = src.Flag('0')
+}
+
+// letters only? No 'p', 'T', or 'w'.
+const verbs = "abcdefghijklmnoqrstuvxyzABCDEFGHIJKLMNOPQRSUVWXYZ"
+
+func FuzzFmtStateString(f *testing.F) {
+	f.Fuzz(func(t *testing.T,
+		width, prec uint8,
+		flagMinus, flagPlus, flagSharp, flagSpace, flagZero bool,
+		verbIdx uint8,
+	) {
+		if flagMinus {
+			flagZero = false
+		}
+		input := FmtState{
+			MWidth:     int(width),
+			MPrec:      int(prec),
+			MFlagMinus: flagMinus,
+			MFlagPlus:  flagPlus,
+			MFlagSharp: flagSharp,
+			MFlagSpace: flagSpace,
+			MFlagZero:  flagZero,
+		}
+		verb := rune(verbs[int(verbIdx)%len(verbs)])
+
+		t.Logf("(%#v, %c) => %q", input, verb, util.FmtStateString(input, verb))
+
+		var output FmtState
+		assert.Equal(t, "", fmt.Sprintf(util.FmtStateString(input, verb), &output))
+		assert.Equal(t, input, output)
+	})
+}