And updated the tests on Windows. It works!

test/allcalls_windows.h

@@ -0,0 +1,5 @@
+// 28 may 2019
+
+// This file should NOT have include guards as it is intended to be included more than once; see noinitwrongthread_windows.c for details.
+
+allcallsCase(uiWindowsControlHandle, NULL)

test/controls_windows.c

@@ -1,8 +1,14 @@
 // 10 june 2019
 #include "test_windows.h"
 
+static HWND osVtableNopHandle(uiControl *c, void *implData)
+{
+	return NULL;
+}
+
 static const uiControlOSVtable osVtable = {
 	.Size = sizeof (uiControlOSVtable),
+	.Handle = osVtableNopHandle,
 };
 
 const uiControlOSVtable *testOSVtable(void)
@@ -23,3 +29,26 @@ Test(WrongControlOSVtableSizeIsProgrammerError)
 	uiRegisterControlType("name", &vtable, &osvt, 0);
 	endCheckProgrammerError(ctx);
 }
+
+Test(ControlOSVtableWithMissingHandleMethodIsProgrammerError)
+{
+	uiControlVtable vtable;
+	uiControlOSVtable osvt;
+	void *ctx;
+
+	testControlLoadNopVtable(&vtable);
+	ctx = beginCheckProgrammerError("uiRegisterControlType(): required uiControlOSVtable method Handle() missing for uiControl type name");
+	osvt = osVtable;
+	osvt.Handle = NULL;
+	uiRegisterControlType("name", &vtable, &osvt, 0);
+	endCheckProgrammerError(ctx);
+}
+
+Test(GettingWindowsHandleOfNullControlIsProgrammerError)
+{
+	void *ctx;
+
+	ctx = beginCheckProgrammerError("uiWindowsControlHandle(): invalid null pointer for uiControl");
+	uiWindowsControlHandle(NULL);
+	endCheckProgrammerError(ctx);
+}

test/meson.build

@@ -13,6 +13,11 @@ libui_allcalls_headers = files([
 if libui_OS == 'windows'
 	libui_test_sources += files([
 		'controls_windows.c',
+		'noinitwrongthread_windows.c',
+		'window_windows.c',
+	])
+	libui_allcalls_headers += files([
+		'allcalls_windows.h',
 	])
 elif libui_OS == 'darwin'
 	libui_test_sources += files([
@@ -51,6 +56,7 @@ libui_test_sources_without_cases = [
 if libui_OS == 'windows'
 	libui_test_sources_without_cases += [
 		'thread_windows.c',
+		'utf8_windows.c',
 		windows.compile_resources('resources_' + libui_mode + '.rc',
 			args: libui_manifest_args,
 			depend_files: ['test_' + libui_mode + '.manifest']),

test/noinitwrongthread_windows.c

@@ -0,0 +1,6 @@
+// 28 may 2019
+#include "test_windows.h"
+#include "thread.h"
+
+#define allcallsHeader "allcalls_windows.h"
+#include "noinitwrongthreadimpl.h"

test/test_windows.h

@@ -3,3 +3,6 @@
 #include "../windows/winapi.hpp"
 #define libuiOSHeader "../ui_windows.h"
 #include "test.h"
+
+// utf8_windows.c
+extern uint16_t *testGetWindowText(HWND hwnd);

test/utf8_windows.c

@@ -0,0 +1,24 @@
+// 7 june 2020
+#include "test_windows.h"
+
+// Do not put any test cases in this file; they will not be run.
+
+uint16_t *testGetWindowText(HWND hwnd)
+{
+	LRESULT n;
+	WCHAR *text;
+
+	n = SendMessageW(hwnd, WM_GETTEXTLENGTH, 0, 0);
+	// WM_GETTEXTLENGTH does not include the null terminator
+	text = (WCHAR *) malloc((n + 1) * sizeof (WCHAR));
+	if (text == NULL)
+		TestFatalf("memory exhausted allocating space for window text");
+	// note the comparison: the size includes the null terminator, but the return does not
+	if (GetWindowTextW(hwnd, text, n + 1) != n) {
+		DWORD le;
+
+		le = GetLastError();
+		TestFatalf("error getting window text; last error %d", le);
+	}
+	return (uint16_t *) text;
+}