test: start adding fuzz testing

src/backend.zig

@@ -157,6 +157,36 @@ test "backend: text field" {
 
     field.setReadOnly(true);
     field.setReadOnly(false);
+
+    try std.testing.fuzz(fuzzTextField, .{});
+}
+
+fn fuzzTextField(input: []const u8) !void {
+    var field = try backend.TextField.create();
+    defer field.deinit();
+    field.setText(input);
+    if (std.unicode.utf8ValidateSlice(input)) {
+        // This constraint only holds if the input is valid UTF-8
+        try std.testing.expectEqualStrings(input, field.getText());
+    }
+}
+
+test "backend: button" {
+    try std.testing.fuzz(fuzzButton, .{});
+}
+
+fn fuzzButton(input: []const u8) !void {
+    var button = try backend.Button.create();
+    defer button.deinit();
+
+    const null_terminated_input = try std.testing.allocator.dupeZ(u8, input);
+    defer std.testing.allocator.free(null_terminated_input);
+
+    button.setLabel(null_terminated_input);
+    if (std.unicode.utf8ValidateSlice(input)) {
+        // This constraint only holds if the input is valid UTF-8
+        try std.testing.expectEqualStrings(null_terminated_input, button.getLabel());
+    }
 }
 
 test "backend: scrollable" {

src/backends/gtk/TextField.zig

@@ -27,7 +27,7 @@ pub fn create() common.BackendError!TextField {
 }
 
 pub fn setText(self: *TextField, text: []const u8) void {
-    var view = std.unicode.Utf8View.initUnchecked(text);
+    var view = std.unicode.Utf8View.init(text) catch return;
     var iterator = view.iterator();
     var numChars: c_int = 0;
     while (iterator.nextCodepoint() != null) {

src/components/TextField.zig

@@ -11,7 +11,7 @@ pub const TextField = struct {
 
     peer: ?backend.TextField = null,
     widget_data: TextField.WidgetData = .{},
-    /// The text this TextField contains
+    /// The text displayed by this TextField. This is assumed to be valid UTF-8.
     text: Atom([]const u8) = Atom([]const u8).of(""),
     /// Whether the TextField is read-only
     readOnly: Atom(bool) = Atom(bool).of(false),