And filled in haiku tests. It builds, but doesn't run.

test/controls_haiku.c

@@ -0,0 +1,11 @@
+// 18 january 2020
+#include "test_haiku.h"
+
+static const uiControlOSVtable vtable = {
+	.Size = sizeof (uiControlOSVtable),
+};
+
+const uiControlOSVtable *testOSVtable(void)
+{
+	return &vtable;
+}

test/controls_haiku_errors.cpp

@@ -0,0 +1,17 @@
+// 18 january 2020
+#include "test_haiku.h"
+
+const struct checkErrorCase controlOSVtableCases[] = {
+	{
+		"uiRegisterControlType() with OS vtable with wrong size",
+		[](void) {
+			uiControlOSVtable vtable;
+		
+			memset(&vtable, 0, sizeof (uiControlOSVtable));
+			vtable.Size = 1;
+			uiRegisterControlType("name", testVtable(), &vtable, 0);
+		},
+		"uiRegisterControlType(): wrong size 1 for uiControlOSVtable",
+	},
+	{ NULL, NULL, NULL },
+};

test/meson.build

@@ -22,7 +22,10 @@ elif libui_OS == 'darwin'
 		'controls_darwin_errors.m',
 	]
 elif libui_OS == 'haiku'
-	# TODO
+	libui_test_sources += [
+		'controls_haiku.c',
+		'controls_haiku_errors.cpp',
+	]
 else
 	libui_test_sources += [
 		'controls_unix.c',

test/test_haiku.h

@@ -0,0 +1,3 @@
+// 18 january 2020
+#define libuiOSHeader "../ui_haiku.h"
+#include "test.h"