Index: unittests/clang-tidy/CMakeLists.txt
===================================================================
--- unittests/clang-tidy/CMakeLists.txt
+++ unittests/clang-tidy/CMakeLists.txt
@@ -12,6 +12,7 @@
   IncludeInserterTest.cpp
   GoogleModuleTest.cpp
   LLVMModuleTest.cpp
+  ModernizerModuleTest.cpp
   NamespaceAliaserTest.cpp
   ObjCModuleTest.cpp
   OverlappingReplacementsTest.cpp
@@ -29,6 +30,7 @@
   clangTidyAndroidModule
   clangTidyGoogleModule
   clangTidyLLVMModule
+  clangTidyModernizeModule
   clangTidyObjCModule
   clangTidyReadabilityModule
   clangTidyUtils
Index: unittests/clang-tidy/ClangTidyTest.h
===================================================================
--- unittests/clang-tidy/ClangTidyTest.h
+++ unittests/clang-tidy/ClangTidyTest.h
@@ -13,6 +13,7 @@
 #include "ClangTidy.h"
 #include "ClangTidyDiagnosticConsumer.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Format/Format.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/FrontendActions.h"
 #include "clang/Tooling/Refactoring.h"
@@ -140,7 +141,32 @@
   }
   if (Errors)
     *Errors = Context.getErrors();
-  auto Result = tooling::applyAllReplacements(Code, Fixes);
+
+  if (Options.FormatStyle) {
+    llvm::Expected<format::FormatStyle> Style = format::getStyle(
+        *Options.FormatStyle, Filename.getSingleStringRef(), "LLVM");
+
+    llvm::Expected<tooling::Replacements> CleannedReplacements =
+        format::cleanupAroundReplacements(Code, Fixes, *Style);
+    if (!CleannedReplacements) {
+      llvm::errs() << llvm::toString(CleannedReplacements.takeError()) << "\n";
+      return "";
+    }
+    if (llvm::Expected<tooling::Replacements> FormattedReplacements =
+            format::formatReplacements(Code, *CleannedReplacements, *Style)) {
+      CleannedReplacements = std::move(FormattedReplacements);
+      if (!CleannedReplacements)
+        return "";
+    } else {
+      llvm::errs() << llvm::toString(FormattedReplacements.takeError())
+                   << ". Skipping formatting.\n";
+      return "";
+    }
+    Fixes = *CleannedReplacements;
+  }
+
+  llvm::Expected<std::string> Result =
+      tooling::applyAllReplacements(Code, Fixes);
   if (!Result) {
     // FIXME: propogate the error.
     llvm::consumeError(Result.takeError());
@@ -149,6 +175,21 @@
   return *Result;
 }
 
+template <typename... CheckList>
+std::string runCheckAndFormatOnCode(
+    StringRef Code, StringRef FormatStyle = "llvm",
+    std::vector<ClangTidyError> *Errors = nullptr,
+    const Twine &Filename = "input.cc", ArrayRef<std::string> ExtraArgs = None,
+    const ClangTidyOptions &ExtraOptions = ClangTidyOptions(),
+    std::map<StringRef, StringRef> PathsToContent =
+        std::map<StringRef, StringRef>()) {
+
+  ClangTidyOptions Options = ExtraOptions;
+  Options.FormatStyle = FormatStyle;
+  return runCheckOnCode<CheckList...>(Code, Errors, Filename, ExtraArgs,
+                                      Options, PathsToContent);
+}
+
 #define EXPECT_NO_CHANGES(Check, Code)                                         \
   EXPECT_EQ(Code, runCheckOnCode<Check>(Code))
 
Index: unittests/clang-tidy/ModernizerModuleTest.cpp
===================================================================
--- /dev/null
+++ unittests/clang-tidy/ModernizerModuleTest.cpp
@@ -0,0 +1,92 @@
+#include "ClangTidyTest.h"
+#include "modernize/UseDefaultMemberInitCheck.h"
+#include "gtest/gtest.h"
+
+using namespace clang::tidy::modernize;
+
+namespace clang {
+namespace tidy {
+namespace test {
+
+TEST(UseDefaultMemberInitCheckTest, NoChanges) {
+  EXPECT_NO_CHANGES(
+      UseDefaultMemberInitCheck,
+      "struct S { S() = default; bool a_ = false; bool b_ = false; };");
+  EXPECT_NO_CHANGES(UseDefaultMemberInitCheck, "struct S { S() : a_(true), "
+                                               "b_(true) {} bool a_{false}; "
+                                               "bool b_{false}; };");
+}
+
+TEST(UseDefaultMemberInitCheckTest, Basic) {
+  EXPECT_EQ("struct S {\n"
+            "  S() {}\n"
+            "  bool a_{false};\n"
+            "};",
+            runCheckAndFormatOnCode<UseDefaultMemberInitCheck>(
+                "struct S { S() : a_(false) {} bool a_; };"));
+}
+
+TEST(UseDefaultMemberInitCheckTest, SeveralInitializers) {
+  EXPECT_EQ(
+      "struct S {\n"
+      "  S() {}\n"
+      "  bool a_{false};\n"
+      "  bool b_{true};\n"
+      "};",
+      runCheckAndFormatOnCode<UseDefaultMemberInitCheck>(
+          "struct S { S() : a_(false), b_(true) {} bool a_; bool b_; };"));
+}
+
+TEST(UseDefaultMemberInitCheckTest, ExceptSpec) {
+  EXPECT_EQ(
+      "struct S {\n"
+      "  S() noexcept(true) {}\n"
+      "  bool a_{false};\n"
+      "  bool b_{true};\n"
+      "};",
+      runCheckAndFormatOnCode<UseDefaultMemberInitCheck>(
+          "struct S { S() noexcept(true) : a_(false), b_(true) {} bool a_; "
+          "bool b_; };"));
+  EXPECT_EQ(
+      "#define NOEXCEPT_(X) noexcept(X)\n"
+      "struct S {\n"
+      "  S() NOEXCEPT_(true) {}\n"
+      "  bool a_{false};\n"
+      "  bool b_{true};\n"
+      "};",
+      runCheckAndFormatOnCode<UseDefaultMemberInitCheck>(
+          "#define NOEXCEPT_(X) noexcept(X)\n"
+          "struct S { S() NOEXCEPT_(true) : a_(false), b_(true) {} bool a_; "
+          "bool b_; };"));
+}
+
+TEST(UseDefaultMemberInitCheckTest, OnExisting) {
+  EXPECT_EQ("struct S {\n"
+            "  S() {}\n"
+            "  bool a_{false};\n"
+            "  bool b_{true};\n"
+            "};",
+            runCheckAndFormatOnCode<UseDefaultMemberInitCheck>(
+                "struct S { S() : a_(false), b_(true) {} bool a_{false}; bool "
+                "b_{true}; };"));
+  EXPECT_EQ("struct S {\n"
+            "  S() : a_(true) {}\n"
+            "  bool a_{false};\n"
+            "  bool b_{true};\n"
+            "};",
+            runCheckAndFormatOnCode<UseDefaultMemberInitCheck>(
+                "struct S { S() : a_(true), b_(true) {} bool a_{false}; bool "
+                "b_{true}; };"));
+  EXPECT_EQ("struct S {\n"
+            "  S() : b_(false) {}\n"
+            "  bool a_{false};\n"
+            "  bool b_{true};\n"
+            "};",
+            runCheckAndFormatOnCode<UseDefaultMemberInitCheck>(
+                "struct S { S() : a_(false), b_(false) {} bool a_{false}; bool "
+                "b_{true}; };"));
+}
+
+} // namespace test
+} // namespace tidy
+} // namespace clang