Add emoji prefix.

build.zig

@@ -82,6 +82,19 @@ pub fn build(b: *std.Build) void {
     });
     tests.root_module.addImport("glib", gobject.module("glib2"));
 
-    const run_tests = b.addRunArtifact(tests);
-    b.step("test", "Run the tests").dependOn(&run_tests.step);
+    const test_step = b.step("test", "Run the tests");
+    test_step.dependOn(&b.addRunArtifact(tests).step);
+
+    // A second root for the same reason, one step further out: `emoji.zig` is a
+    // table and a search over it, and it imports nothing at all. It cannot hang
+    // off the root above because a test binary has exactly one root, and
+    // Layouts.zig has no reason to reach for the emoji table.
+    const emoji_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path("src/emoji.zig"),
+            .target = target,
+            .optimize = optimize,
+        }),
+    });
+    test_step.dependOn(&b.addRunArtifact(emoji_tests).step);
 }