Index: clang-tools-extra/test/clang-tidy/infrastructure/run-clang-tidy.cpp
===================================================================
--- clang-tools-extra/test/clang-tidy/infrastructure/run-clang-tidy.cpp
+++ /dev/null
@@ -1,18 +0,0 @@
-// RUN: %run_clang_tidy --help
-// RUN: rm -rf %t
-// RUN: mkdir %t
-// RUN: echo "[{\"directory\":\".\",\"command\":\"clang++ -c %/t/test.cpp\",\"file\":\"%/t/test.cpp\"}]" | sed -e 's/\\/\\\\/g' > %t/compile_commands.json
-// RUN: echo "Checks: '-*,modernize-use-auto'" > %t/.clang-tidy
-// RUN: echo "WarningsAsErrors: '*'" >> %t/.clang-tidy
-// RUN: echo "CheckOptions:" >> %t/.clang-tidy
-// RUN: echo "  - key:             modernize-use-auto.MinTypeNameLength" >> %t/.clang-tidy
-// RUN: echo "    value:           '0'" >> %t/.clang-tidy
-// RUN: cp "%s" "%t/test.cpp"
-// RUN: cd "%t"
-// RUN: not %run_clang_tidy "test.cpp"
-
-int main()
-{
-  int* x = new int();
-  delete x;
-}
Index: clang-tools-extra/test/clang-tidy/infrastructure/run-clang-tidy_config-file.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/infrastructure/run-clang-tidy_config-file.cpp
@@ -0,0 +1,33 @@
+// under test:
+// - .clang-tidy read from file & treat warnings as errors
+// - return code of run-clang-tidy on those errors
+
+// First make sure clang-tidy is executable and can print help without crashing:
+// RUN: %run_clang_tidy --help
+
+// use %t as directory instead of file:
+// RUN: rm -rf %t
+// RUN: mkdir %t
+
+// add this file to %t, add compile_commands for it and .clang-tidy config:
+// RUN: echo "[{\"directory\":\".\",\"command\":\"clang++ -c %/t/test.cpp\",\"file\":\"%/t/test.cpp\"}]" | sed -e 's/\\/\\\\/g' > %t/compile_commands.json
+// RUN: echo "Checks: '-*,modernize-use-auto'" > %t/.clang-tidy
+// RUN: echo "WarningsAsErrors: '*'" >> %t/.clang-tidy
+// RUN: echo "CheckOptions:" >> %t/.clang-tidy
+// RUN: echo "  - key:             modernize-use-auto.MinTypeNameLength" >> %t/.clang-tidy
+// RUN: echo "    value:           '0'" >> %t/.clang-tidy
+// RUN: cp "%s" "%t/test.cpp"
+
+// execute and check:
+// RUN: cd "%t"
+// RUN: not %run_clang_tidy "test.cpp" > %t/msg.txt 2>&1
+// RUN: FileCheck -input-file=%t/msg.txt -check-prefix=CHECK-MESSAGES %s \
+// RUN:           -implicit-check-not='{{warning|error|note}}:'
+
+int main()
+{
+  int* x = new int();
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: error: {{.+}} [modernize-use-auto,-warnings-as-errors]
+
+  delete x;
+}
Index: clang-tools-extra/test/clang-tidy/infrastructure/run-clang-tidy_export-diagnostics.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/infrastructure/run-clang-tidy_export-diagnostics.cpp
@@ -0,0 +1,33 @@
+// under test:
+// - parsing and using compile_commands
+// - export fixes to yaml file
+
+// use %t as directory instead of file,
+// because "compile_commands.json" must have exactly that name:
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: echo '[{"directory":"%/S","command":"clang++ -c %s","file":"%s"}]' \
+// RUN:      > %t/compile_commands.json
+
+// execute and check:
+// RUN: cd "%t"
+// RUN: %run_clang_tidy -checks='-*,bugprone-sizeof-container,modernize-use-auto' \
+// RUN:                 -p="%/t" -export-fixes=%t/fixes.yaml > %t/msg.txt 2>&1
+// RUN: FileCheck -input-file=%t/msg.txt -check-prefix=CHECK-MESSAGES %s \
+// RUN:           -implicit-check-not='{{warning|error|note}}:'
+// RUN: FileCheck -input-file=%t/fixes.yaml -check-prefix=CHECK-YAML %s
+
+#include <vector>
+int main()
+{
+  std::vector<int> vec;
+  std::vector<int>::iterator iter = vec.begin();
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use auto when declaring iterators
+  // CHECK-YAML: modernize-use-auto
+  
+  return sizeof(vec);
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: sizeof() doesn't return the size of the container; did you mean .size()? [bugprone-sizeof-container]
+  // CHECK-YAML: bugprone-sizeof-container
+  // After https://reviews.llvm.org/D72730 --> CHECK-YAML-NOT: bugprone-sizeof-container
+}
+