diff --git a/change/react-native-windows-2020-04-29-03-21-18-testhook.json b/change/react-native-windows-2020-04-29-03-21-18-testhook.json
new file mode 100644
index 00000000000..3e1c6f1a455
--- /dev/null
+++ b/change/react-native-windows-2020-04-29-03-21-18-testhook.json
@@ -0,0 +1,8 @@
+{
+  "type": "prerelease",
+  "comment": "Refactor TestHook out of ViewManagerBase and special case layout properties",
+  "packageName": "react-native-windows",
+  "email": "asklar@microsoft.com",
+  "dependentChangeType": "patch",
+  "date": "2020-04-29T10:21:18.921Z"
+}
diff --git a/vnext/Microsoft.ReactNative/Microsoft.ReactNative.vcxproj b/vnext/Microsoft.ReactNative/Microsoft.ReactNative.vcxproj
index c5e68931833..57d6d88ea13 100644
--- a/vnext/Microsoft.ReactNative/Microsoft.ReactNative.vcxproj
+++ b/vnext/Microsoft.ReactNative/Microsoft.ReactNative.vcxproj
@@ -331,6 +331,7 @@
     </ClInclude>
     <ClInclude Include="RedBox.h" />
     <ClInclude Include="ReactSupport.h" />
+    <ClInclude Include="TestHook.h" />
     <ClInclude Include="Threading\BatchingQueueThread.h" />
     <ClInclude Include="Threading\MessageDispatchQueue.h" />
     <ClInclude Include="Threading\MessageQueueThreadFactory.h" />
@@ -488,6 +489,7 @@
     </ClCompile>
     <ClCompile Include="RedBox.cpp" />
     <ClCompile Include="ReactSupport.cpp" />
+    <ClCompile Include="TestHook.cpp" />
     <ClCompile Include="Threading\BatchingQueueThread.cpp" />
     <ClCompile Include="Threading\MessageDispatchQueue.cpp" />
     <ClCompile Include="Threading\MessageQueueThreadFactory.cpp" />
diff --git a/vnext/Microsoft.ReactNative/Microsoft.ReactNative.vcxproj.filters b/vnext/Microsoft.ReactNative/Microsoft.ReactNative.vcxproj.filters
index 3b221e531d0..e53f5484d2f 100644
--- a/vnext/Microsoft.ReactNative/Microsoft.ReactNative.vcxproj.filters
+++ b/vnext/Microsoft.ReactNative/Microsoft.ReactNative.vcxproj.filters
@@ -92,9 +92,6 @@
     <ClCompile Include="..\ReactUWP\Modules\AppThemeModuleUwp.cpp">
       <Filter>Modules</Filter>
     </ClCompile>
-    <ClCompile Include="..\ReactUWP\Modules\ClipboardModule.cpp">
-      <Filter>Modules</Filter>
-    </ClCompile>
     <ClCompile Include="..\ReactUWP\Modules\DeviceInfoModule.cpp">
       <Filter>Modules</Filter>
     </ClCompile>
@@ -318,6 +315,8 @@
     <ClCompile Include="Views\ReactRootControl.cpp">
       <Filter>Views</Filter>
     </ClCompile>
+    <ClCompile Include="Modules\ClipboardModule.cpp" />
+    <ClCompile Include="TestHook.cpp" />
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="..\ReactUWP\Base\CoreNativeModules.h">
@@ -410,9 +409,6 @@
     <ClInclude Include="..\ReactUWP\Modules\AppThemeModuleUwp.h">
       <Filter>Modules</Filter>
     </ClInclude>
-    <ClInclude Include="..\ReactUWP\Modules\ClipboardModule.h">
-      <Filter>Modules</Filter>
-    </ClInclude>
     <ClInclude Include="..\ReactUWP\Modules\DeviceInfoModule.h">
       <Filter>Modules</Filter>
     </ClInclude>
@@ -674,6 +670,8 @@
     <ClInclude Include="Views\ReactRootControl.h">
       <Filter>Views</Filter>
     </ClInclude>
+    <ClInclude Include="Modules\ClipboardModule.h" />
+    <ClInclude Include="TestHook.h" />
   </ItemGroup>
   <ItemGroup>
     <Midl Include="..\ReactUWP\Views\cppwinrt\AccessibilityAction.idl">
diff --git a/vnext/Microsoft.ReactNative/TestHook.cpp b/vnext/Microsoft.ReactNative/TestHook.cpp
new file mode 100644
index 00000000000..dc686a34c3f
--- /dev/null
+++ b/vnext/Microsoft.ReactNative/TestHook.cpp
@@ -0,0 +1,103 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+#include "pch.h"
+#include "TestHook.h"
+#include <cdebug.h>
+
+#ifdef DEBUG
+
+// Obtained from https://reactnative.dev/docs/layout-props
+// See getLayoutProps.ps1 next to this file.
+std::vector<std::string> TestHook::layoutProperties = {
+    "alignContent",
+    "alignItems",
+    "alignSelf",
+    "aspectRatio",
+    "borderBottomWidth",
+    "borderEndWidth",
+    "borderLeftWidth",
+    "borderRightWidth",
+    "borderStartWidth",
+    "borderTopWidth",
+    "borderWidth",
+    "bottom",
+    "direction",
+    "display",
+    "end",
+    "flex",
+    "flexBasis",
+    "flexDirection",
+    "flexGrow",
+    "flexShrink",
+    "flexWrap",
+    "height",
+    "justifyContent",
+    "left",
+    "margin",
+    "marginBottom",
+    "marginEnd",
+    "marginHorizontal",
+    "marginLeft",
+    "marginRight",
+    "marginStart",
+    "marginTop",
+    "marginVertical",
+    "maxHeight",
+    "maxWidth",
+    "minHeight",
+    "minWidth",
+    "overflow",
+    "padding",
+    "paddingBottom",
+    "paddingEnd",
+    "paddingHorizontal",
+    "paddingLeft",
+    "paddingRight",
+    "paddingStart",
+    "paddingTop",
+    "paddingVertical",
+    "position",
+    "right",
+    "start",
+    "top",
+    "width",
+    "zIndex",
+};
+
+void TestHook::NotifyUnimplementedProperty(
+    const std::string &viewManager,
+    const std::string &reactClassName,
+    const std::string &propertyName,
+    const folly::dynamic &propertyValue) {
+  if (std::find(layoutProperties.begin(), layoutProperties.end(), propertyName) != layoutProperties.end()) {
+    return;
+  }
+  std::string value;
+  size_t size{};
+  try {
+    if (propertyValue.isObject()) {
+      value = "[Object]";
+    } else if (propertyValue.isNull()) {
+      value = "[Null]";
+    } else if (propertyValue.isArray()) {
+      size = propertyValue.size();
+      value = "[Array]";
+    } else {
+      value = propertyValue.asString();
+    }
+  } catch (const folly::TypeError &e) {
+    value = e.what();
+  }
+
+  cdebug << "[UnimplementedProperty] ViewManager = " << viewManager << " elementClass = " << reactClassName
+         << " propertyName = " << propertyName << " value = " << value;
+
+  if (size != 0) {
+    cdebug << " (" << size << " elems)";
+  }
+
+  cdebug << std::endl;
+  // DebugBreak();
+}
+
+#endif // DEBUG
diff --git a/vnext/Microsoft.ReactNative/TestHook.h b/vnext/Microsoft.ReactNative/TestHook.h
new file mode 100644
index 00000000000..c5dc3983a1c
--- /dev/null
+++ b/vnext/Microsoft.ReactNative/TestHook.h
@@ -0,0 +1,15 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+#pragma once
+#include <folly/dynamic.h>
+#include <string>
+#include <vector>
+
+struct TestHook {
+  static void NotifyUnimplementedProperty(
+      const std::string &viewManager,
+      const std::string &reactClassName,
+      const std::string &propertyName,
+      const folly::dynamic &propertyValue);
+  static std::vector<std::string> layoutProperties;
+};
diff --git a/vnext/Microsoft.ReactNative/getLayoutProps.ps1 b/vnext/Microsoft.ReactNative/getLayoutProps.ps1
new file mode 100644
index 00000000000..0a222f0219e
--- /dev/null
+++ b/vnext/Microsoft.ReactNative/getLayoutProps.ps1
@@ -0,0 +1,5 @@
+# This script produces the values for the layoutProperties vector
+# in TestHook.cpp
+$page = Invoke-WebRequest "https://reactnative.dev/docs/layout-props"
+$lines = $page.Content.Split('</a><code>') | select -skip 1
+$lines -replace ('\n','')  -replace ('</code>.*', '') | % { Write-Host "`"$_`", "}
\ No newline at end of file
diff --git a/vnext/ReactUWP/ReactUWP.vcxproj b/vnext/ReactUWP/ReactUWP.vcxproj
index 03c65e65794..b1882e5948e 100644
--- a/vnext/ReactUWP/ReactUWP.vcxproj
+++ b/vnext/ReactUWP/ReactUWP.vcxproj
@@ -119,7 +119,8 @@
         $(ReactNativeWindowsDir)Shared;
         $(ReactNativeWindowsDir)stubs;
         $(YogaDir);
-        %(AdditionalIncludeDirectories)
+        %(AdditionalIncludeDirectories);
+        $(ReactNativeWindowsDir)Microsoft.ReactNative;
       </AdditionalIncludeDirectories>
       <AdditionalIncludeDirectories Condition="'$(CHAKRACOREUWP)'=='true'">$(ChakraCoreInclude);$(ChakraCoreDebugInclude);%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <AdditionalOptions>/await %(AdditionalOptions)</AdditionalOptions>
@@ -280,6 +281,7 @@
     <ClCompile Include="Modules\Animated\SpringAnimationDriver.cpp" />
     <ClCompile Include="Modules\Animated\TrackingAnimatedNode.cpp" />
     <ClCompile Include="Modules\AppearanceModule.cpp" />
+    <ClCompile Include="TestHookMock.cpp" />
     <ClCompile Include="Threading\BatchingUIMessageQueueThread.cpp" />
     <ClCompile Include="Threading\MessageQueueThreadFactory.cpp" />
     <ClCompile Include="TurboModule\TurboModuleUtils.cpp" />
diff --git a/vnext/ReactUWP/ReactUWP.vcxproj.filters b/vnext/ReactUWP/ReactUWP.vcxproj.filters
index 72f9ca1a9bc..30f2d7c7f54 100644
--- a/vnext/ReactUWP/ReactUWP.vcxproj.filters
+++ b/vnext/ReactUWP/ReactUWP.vcxproj.filters
@@ -323,6 +323,7 @@
       <Filter>Views</Filter>
     </ClCompile>
     <ClCompile Include="Modules\AppearanceModule.cpp" />
+    <ClCompile Include="TestHookMock.cpp" />
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="..\include\ReactUWP\InstanceFactory.h">
diff --git a/vnext/ReactUWP/TestHookMock.cpp b/vnext/ReactUWP/TestHookMock.cpp
new file mode 100644
index 00000000000..7a5af1951d7
--- /dev/null
+++ b/vnext/ReactUWP/TestHookMock.cpp
@@ -0,0 +1,7 @@
+#include "TestHook.h"
+
+void TestHook::NotifyUnimplementedProperty(
+    const std::string &,
+    const std::string &,
+    const std::string &,
+    const folly::dynamic &) {}
diff --git a/vnext/ReactUWP/Views/ViewManagerBase.cpp b/vnext/ReactUWP/Views/ViewManagerBase.cpp
index 9723ceca252..239be0a7da4 100644
--- a/vnext/ReactUWP/Views/ViewManagerBase.cpp
+++ b/vnext/ReactUWP/Views/ViewManagerBase.cpp
@@ -13,6 +13,7 @@
 
 #include <IReactInstance.h>
 #include <IXamlRootView.h>
+#include <TestHook.h>
 #include <Views/ShadowNodeBase.h>
 
 using namespace folly;
@@ -275,43 +276,6 @@ void ViewManagerBase::NotifyUnimplementedProperty(
 #endif // DEBUG
 }
 
-#ifdef DEBUG
-
-void ViewManagerBase::TestHook::NotifyUnimplementedProperty(
-    const std::string &viewManager,
-    const std::string &reactClassName,
-    const std::string &propertyName,
-    const folly::dynamic &propertyValue) {
-  std::string value;
-  size_t size{};
-  try {
-    if (propertyValue.isObject()) {
-      value = "[Object]";
-    } else if (propertyValue.isNull()) {
-      value = "[Null]";
-    } else if (propertyValue.isArray()) {
-      size = propertyValue.size();
-      value = "[Array]";
-    } else {
-      value = propertyValue.asString();
-    }
-  } catch (const TypeError &e) {
-    value = e.what();
-  }
-
-  cdebug << "[UnimplementedProperty] ViewManager = " << viewManager << " elementClass = " << reactClassName
-         << " propertyName = " << propertyName << " value = " << value;
-
-  if (size != 0) {
-    cdebug << " (" << size << " elems)";
-  }
-
-  cdebug << std::endl;
-  // DebugBreak();
-}
-
-#endif // DEBUG
-
 void ViewManagerBase::SetLayoutProps(
     ShadowNodeBase &nodeToUpdate,
     const XamlView &viewToUpdate,
diff --git a/vnext/include/ReactUWP/Views/ViewManagerBase.h b/vnext/include/ReactUWP/Views/ViewManagerBase.h
index ea959424f1c..fab7fad114e 100644
--- a/vnext/include/ReactUWP/Views/ViewManagerBase.h
+++ b/vnext/include/ReactUWP/Views/ViewManagerBase.h
@@ -92,15 +92,7 @@ class REACTWINDOWS_EXPORT ViewManagerBase : public facebook::react::IViewManager
       ShadowNodeBase *nodeToUpdate,
       const std::string &propertyName,
       const folly::dynamic &value);
-#ifdef DEBUG
-  struct TestHook {
-    static void NotifyUnimplementedProperty(
-        const std::string &viewManager,
-        const std::string &reactClassName,
-        const std::string &propertyName,
-        const folly::dynamic &propertyValue);
-  };
-#endif
+
  protected:
   std::weak_ptr<IReactInstance> m_wkReactInstance;
 };