[test-improver] Improve tests for strutil.RandomHex

internal/strutil/random_hex_test.go

@@ -1,6 +1,7 @@
 package strutil
 
 import (
+	"encoding/hex"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -12,7 +13,18 @@ func TestRandomHex(t *testing.T) {
 		name    string
 		n       int
 		wantLen int
+		wantErr bool
 	}{
+		{
+			name:    "zero bytes produces empty string",
+			n:       0,
+			wantLen: 0,
+		},
+		{
+			name:    "1 byte produces 2 hex chars",
+			n:       1,
+			wantLen: 2,
+		},
 		{
 			name:    "16 bytes produces 32 hex chars",
 			n:       16,
@@ -24,21 +36,49 @@ func TestRandomHex(t *testing.T) {
 			wantLen: 64,
 		},
 		{
-			name:    "1 byte produces 2 hex chars",
-			n:       1,
-			wantLen: 2,
+			name:    "negative n returns error",
+			n:       -1,
+			wantErr: true,
+		},
+		{
+			name:    "large negative n returns error",
+			n:       -100,
+			wantErr: true,
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			result, err := RandomHex(tt.n)
+			if tt.wantErr {
+				require.Error(t, err)
+				assert.Empty(t, result, "result should be empty on error")
+				return
+			}
 			require.NoError(t, err)
 			assert.Len(t, result, tt.wantLen)
 		})
 	}
 }
 
+// TestRandomHex_ErrorMessageContainsSize verifies the error for negative n includes the invalid value.
+func TestRandomHex_ErrorMessageContainsSize(t *testing.T) {
+	_, err := RandomHex(-5)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "-5", "error message should include the invalid size")
+}
+
+// TestRandomHex_IsValidHex verifies the output is a valid lowercase hex-encoded string
+// and that decoding it yields exactly n bytes.
+func TestRandomHex_IsValidHex(t *testing.T) {
+	result, err := RandomHex(16)
+	require.NoError(t, err)
+
+	decoded, decodeErr := hex.DecodeString(result)
+	require.NoError(t, decodeErr, "result should be valid hex-encoded string")
+	assert.Len(t, decoded, 16, "decoded bytes should have length equal to input n")
+}
+
 func TestRandomHex_Uniqueness(t *testing.T) {
 	seen := make(map[string]bool)
 	for i := 0; i < 100; i++ {