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| -rw-r--r-- | docs/TestingGuide.rst | 37 |
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diff --git a/docs/TestingGuide.rst b/docs/TestingGuide.rst index f66cae1..f26d1bf 100644 --- a/docs/TestingGuide.rst +++ b/docs/TestingGuide.rst @@ -262,6 +262,43 @@ recommended way to examine output to figure out if the test passes it using the :doc:`FileCheck tool <CommandGuide/FileCheck>`. The usage of ``grep`` in RUN lines is discouraged. +Fragile tests +------------- + +It is easy to write a fragile test that would fail spuriously if the tool being +tested outputs a full path to the input file. For example, :program:`opt` by +default outputs a ``ModuleID``: + +.. code-block:: console + + $ cat example.ll + define i32 @main() nounwind { + ret i32 0 + } + + $ opt -S /path/to/example.ll + ; ModuleID = '/path/to/example.ll' + + define i32 @main() nounwind { + ret i32 0 + } + +``ModuleID`` can unexpetedly match against ``CHECK`` lines. For example: + +.. code-block:: llvm + + ; RUN: opt -S %s | FileCheck + + define i32 @main() nounwind { + ; CHECK-NOT: load + ret i32 0 + } + +This test will fail if placed into a ``download`` directory. + +To make your tests robust, always use ``opt ... < %s`` in the RUN line. +:program:`opt` does not output a ``ModuleID`` when input comes from stdin. + The FileCheck utility --------------------- |