[clang-tidy] Organized clang-tidy unit tests. NFC.

  * Moved unit tests for BracesAroundStatementsCheck to
    ReadabilityModuleTest.cpp.
  * Moved EXPECT_NO_CHANGES macro to ClangTidyTest.h to avoid defining it three
    times.

llvm-svn: 230947
diff --git a/clang-tools-extra/unittests/clang-tidy/ClangTidyTest.h b/clang-tools-extra/unittests/clang-tidy/ClangTidyTest.h
index 54a38c4..a90d557 100644
--- a/clang-tools-extra/unittests/clang-tidy/ClangTidyTest.h
+++ b/clang-tools-extra/unittests/clang-tidy/ClangTidyTest.h
@@ -78,6 +78,9 @@
   return tooling::applyAllReplacements(Code, Fixes);
 }
 
+#define EXPECT_NO_CHANGES(Check, Code)                                         \
+  EXPECT_EQ(Code, runCheckOnCode<Check>(Code))
+
 } // namespace test
 } // namespace tidy
 } // namespace clang