diff --git a/build.zig b/build.zig
index 2a47b70136549550f9f536c7a9a872e046d5c5cc..8a3036d41ff085d7245ec00ed051b22ba68b95c2 100644
--- a/build.zig
+++ b/build.zig
@@ -23,4 +23,11 @@ pub fn build(b: *std.build.Builder) void {
         run_step.dependOn(&run_cmd.step);
     }
 
+    {
+        const t = b.addTest("main.zig");
+        deps.addAllTo(t);
+
+        const t_step = b.step("test", "");
+        t_step.dependOn(&t.step);
+    }
 }
diff --git a/main.zig b/main.zig
index d29869ff88feb94cd5a5fd28d760824920f269ac..220dc52c97a25ba151111466c5edec6350ee746a 100644
--- a/main.zig
+++ b/main.zig
@@ -1,5 +1,21 @@
 const std = @import("std");
+const string = []const u8;
+const time = @import("time");
 
-pub fn main() anyerror!void {
+pub fn main() !void {
     std.log.info("All your codebase are belong to us.", .{});
 }
+
+fn assertOk(input: u64, expected: string) !void {
+    const alloc = std.testing.allocator;
+
+    const actual = try time.DateTime.initUnix(input).formatAlloc(alloc, "YYYY-MM-DD HH:mm:ss");
+    defer alloc.free(actual);
+
+    try std.testing.expectEqualStrings(expected, actual);
+}
+
+// zig fmt: off
+test { try assertOk(0, "1970-01-01 00:00:00"); }
+test { try assertOk(1257894000, "2009-11-10 23:00:00"); }
+test { try assertOk(1634858430, "2021-10-21 23:20:30"); }