[Qemu-devel] [PATCH] qemu-iotests: add a "how to" to ./README

[Stefan Hajnoczi <stefanha@redhat.com>]

There is not much getting started documentation for qemu-iotests.  This
patch explains how to create a new test and covers the overall testing
approach.

Cc: Ishani Chugh <chugh.ishani@research.iiit.ac.in>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 tests/qemu-iotests/README | 83 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/tests/qemu-iotests/README b/tests/qemu-iotests/README
index 6079b40..8259b9f 100644
--- a/tests/qemu-iotests/README
+++ b/tests/qemu-iotests/README
@@ -14,8 +14,91 @@ Just run ./check to run all tests for the raw image format, or ./check
 -qcow2 to test the qcow2 image format.  The output of ./check -h explains
 additional options to test further image formats or I/O methods.
 
+* Testing approach
+
+Each test is an executable file (usually a bash script) that is run by the
+./check test harness.  Standard out and standard error are captured to an
+output file.  If the output file differs from the "golden master" output file
+for the test then it fails.
+
+Tests are simply a sequence of commands that produce output and the test itself
+does not judge whether it passed or failed.  If you find yourself writing
+checks to determine success or failure then you should rethink the test and
+rely on output diffing instead.
+
+** Filtering volatile output
+
+When output contains absolute file paths, timestamps, process IDs, hostnames,
+or other volatile strings, the diff against golden master output will fail.
+Such output must be filtered to replace volatile strings with fixed
+placeholders.
+
+For example, the path to the temporary working directory changes between test
+runs so it must be filtered:
+
+  sed -e "s#$TEST_DIR/#TEST_DIR/#g"
+
+Commonly needed filters are available in ./common.filter.
+
+** Python tests
+
+Most tests are implemented in bash but it is difficult to interact with the QMP
+monitor.  A Python module called 'iotests' is available for tests that require
+JSON and interacting with QEMU.
+
+* How to create a test
+
+1. Choose an unused test number
+
+Tests are identified by a unique number.  Look for the highest test case number
+by looking at the test files.  Then search the qemu-devel@nongnu.org mailing
+list to check if anyone has already sent patches using the next available
+number.  You may need to increment the number a few times to reach an unused
+number.
+
+2. Create the test file
+
+Copy an existing test (one that most closely resembles what you wish to test)
+to the new test number:
+
+  cp 001 <test-number>
+
+3. Assign groups to the test
+
+Add your test to the ./group file.  This file is the index of tests and assigns
+them to functional groups like "rw" for read-write tests.  Most tests belong to
+the "rw" and "auto" groups.  "auto" means the test runs when ./check is invoked
+without a -g argument.
+
+Consider adding your test to the "quick" group if it executes quickly (<1s).
+This group is run by "make check-block" and is often included as part of build
+tests in continuous integration systems.
+
+4. Write the test
+
+Edit the test script.  Look at existing tests for examples.
+
+5. Generate the golden master file
+
+Run your test with "./check <test-number>".  You may need to pass additional
+options to use an image format or protocol.
+
+The test will fail because there is no golden master yet.  Inspect the output
+that your test generated with "cat <test-number>.out.bad".
+
+Verify that the output is as expected and contains no volatile strings like
+timestamps.  You may need to add filters to your test to remove volatile
+strings.
+
+Once you are happy with the test output it can be used as the golden master
+with "mv <test-number>.out.bad <test-number>.out".  Rerun the test to verify
+that it passes.
+
+Congratulations, you've created a new test!
+
 * Feedback and patches
 
 Please send improvements to the test suite, general feedback or just
 reports of failing tests cases to qemu-devel@nongnu.org with a CC:
 to qemu-block@nongnu.org.
+
-- 
2.9.4