add Battery test

src/main.zig

@@ -410,6 +410,7 @@ pub const Battery = struct {
     pub fn init(allocator: std.mem.Allocator) !*Battery {
         var self = try allocator.create(Battery);
         errdefer allocator.destroy(self);
+        self.* = .{ .component = undefined };
         try Component.init(&self.component, allocator, "Battery", 0, 1, &update, &deinit);
         return self;
     }
@@ -427,6 +428,32 @@ pub const Battery = struct {
     }
 };
 
+test "Battery" {
+    var battery = try Battery.init(std.testing.allocator);
+    defer battery.component.deinit(std.testing.allocator);
+
+    // default in-game is 100%
+    // the default should be the same here too
+    try battery.component.update();
+    try std.testing.expectEqual(Signal{ .digital = 1, .analog = 1.0 }, battery.component.getOutput(0).*);
+
+    battery.value = 0.0;
+    try battery.component.update();
+    try std.testing.expectEqual(Signal{ .digital = 0, .analog = 0.0 }, battery.component.getOutput(0).*);
+
+    battery.value = -1.0;
+    try battery.component.update();
+    try std.testing.expectEqual(Signal{ .digital = -1, .analog = -1.0 }, battery.component.getOutput(0).*);
+
+    battery.value = 0.42;
+    try battery.component.update();
+    try std.testing.expectEqual(Signal{ .digital = 1, .analog = 0.42 }, battery.component.getOutput(0).*);
+
+    battery.value = -0.69;
+    try battery.component.update();
+    try std.testing.expectEqual(Signal{ .digital = -1, .analog = -0.69 }, battery.component.getOutput(0).*);
+}
+
 pub const Not = struct {
     component: Component,