Add tests for Entity get/set functions

src/entity.zig

@@ -342,3 +342,78 @@ pub fn Entity(comptime ctx: anytype) type {
         }
     };
 }
+
+const expect = @import("./test/expect.zig");
+
+test "Entity get and set" {
+    flecs.init(std.testing.allocator);
+    var world = try flecs.World(void).initMinimal();
+    defer world.deinit();
+
+    const Position = struct { x: f32, y: f32 };
+    const Velocity = struct { x: f32, y: f32 };
+    _ = try world.component(Position);
+    _ = try world.component(Velocity);
+
+    const entity = try world.entity(.{}, .{});
+
+    entity.set(Position, .{ .x = 10, .y = 20 });
+    entity.set(Velocity, .{ .x = 1, .y = 2 });
+
+    const pos = entity.get(Position).?;
+    const vel = entity.get(Velocity).?;
+
+    entity.set(Position, .{ .x = pos.x + vel.x, .y = pos.y + vel.y });
+
+    try expect.equal(.{ .x = 11, .y = 22 }, entity.get(Position).?);
+}
+
+test "Entity getMut" {
+    flecs.init(std.testing.allocator);
+    var world = try flecs.World(void).initMinimal();
+    defer world.deinit();
+
+    const Position = struct { x: f32, y: f32 };
+    const Velocity = struct { x: f32, y: f32 };
+    _ = try world.component(Position);
+    _ = try world.component(Velocity);
+
+    const entity = try world.entity(.{}, .{ Position, Velocity });
+
+    // Position and Velocity need to be present on the entity for component
+    // pointers to be stable. Otherwise, when `Velocity` is added, the entity
+    // would move tables and invalidate the `Position` pointer.
+
+    const pos = entity.getMut(Position);
+    const vel = entity.getMut(Velocity);
+
+    pos.* = .{ .x = 10, .y = 20 };
+    vel.* = .{ .x = 1, .y = 2 };
+
+    pos.* = .{ .x = pos.x + vel.x, .y = pos.y + vel.y };
+
+    try expect.equal(.{ .x = 11, .y = 22 }, pos.*);
+}
+
+test "Entity set and get with pair type" {
+    flecs.init(std.testing.allocator);
+    var world = try flecs.World(void).initMinimal();
+    defer world.deinit();
+
+    const Position = struct { x: f32, y: f32 };
+    const Rank = struct { value: i32 }; // Gives a component a certain "rank".
+    const Copy = struct {}; // Stores a "copy" of another component.
+    _ = try world.component(Position);
+    _ = try world.component(Rank);
+    _ = try world.tag(Copy);
+
+    const entity = try world.entity(.{}, .{});
+
+    entity.set(Position, .{ .x = 10, .y = 20 });
+    entity.set(.{ Rank, Position }, .{ .value = 9001 });
+    entity.set(.{ Copy, Position }, .{ .x = 60, .y = 80 });
+
+    try expect.equal(.{ .x = 10, .y = 20 }, entity.get(Position));
+    try expect.equal(.{ .value = 9001 }, entity.get(.{ Rank, Position }));
+    try expect.equal(.{ .x = 60, .y = 80 }, entity.get(.{ Copy, Position }));
+}