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+# Unit Tests in GlusterFS
+
+## Overview
+[Art-of-unittesting][definitionofunittest] provides a good definition for unit tests. A good unit test is:
+
+* Able to be fully automated
+* Has full control over all the pieces running (Use mocks or stubs to achieve this isolation when needed)
+* Can be run in any order if part of many other tests
+* Runs in memory (no DB or File access, for example)
+* Consistently returns the same result (You always run the same test, so no random numbers, for example. save those for integration or range tests)
+* Runs fast
+* Tests a single logical concept in the system
+* Readable
+* Maintainable
+* Trustworthy (when you see its result, you don’t need to debug the code just to be sure)
+
+## Cmockery2
+GlusterFS unit test framework is based on [Cmockery2][]. Cmockery provides developers with methods to isolate and test modules written in C language. It also provides integration with Jenkins by providing JUnit XML compliant unit test results.
+
+Before continuing, you may want to familiarize yourself with Cmockery2 by reading the [usage guide][cmockery2usage].
+
+## Running Unit Tests
+To execute the unit tests, all you need is to type `make check`. Here is a step-by-step example assuming you just cloned a GlusterFS tree:
+
+```
+$ ./autogen.sh
+$ ./configure --enable-debug
+$ make check
+```
+
+Sample output:
+
+```
+PASS: mem_pool_unittest
+============================================================================
+Testsuite summary for glusterfs 3git
+============================================================================
+# TOTAL: 1
+# PASS: 1
+# SKIP: 0
+# XFAIL: 0
+# FAIL: 0
+# XPASS: 0
+# ERROR: 0
+============================================================================
+```
+
+In this example, `mem_pool_unittest` has multiple tests inside, but `make check` assumes that the program itself is the test, and that is why it only shows one test. Here is the output when we run `mem_pool_unittest` directly:
+
+```
+$ ./libglusterfs/src/mem_pool_unittest
+[==========] Running 10 test(s).
+[ RUN ] test_gf_mem_acct_enable_set
+Expected assertion data != ((void *)0) occurred
+[ OK ] test_gf_mem_acct_enable_set
+[ RUN ] test_gf_mem_set_acct_info_asserts
+Expected assertion xl != ((void *)0) occurred
+Expected assertion size > ((4 + sizeof (size_t) + sizeof (xlator_t *) + 4 + 8) + 8) occurred
+Expected assertion type <= xl->mem_acct.num_types occurred
+[ OK ] test_gf_mem_set_acct_info_asserts
+[ RUN ] test_gf_mem_set_acct_info_memory
+[ OK ] test_gf_mem_set_acct_info_memory
+[ RUN ] test_gf_calloc_default_calloc
+[ OK ] test_gf_calloc_default_calloc
+[ RUN ] test_gf_calloc_mem_acct_enabled
+[ OK ] test_gf_calloc_mem_acct_enabled
+[ RUN ] test_gf_malloc_default_malloc
+[ OK ] test_gf_malloc_default_malloc
+[ RUN ] test_gf_malloc_mem_acct_enabled
+[ OK ] test_gf_malloc_mem_acct_enabled
+[ RUN ] test_gf_realloc_default_realloc
+[ OK ] test_gf_realloc_default_realloc
+[ RUN ] test_gf_realloc_mem_acct_enabled
+[ OK ] test_gf_realloc_mem_acct_enabled
+[ RUN ] test_gf_realloc_ptr
+Expected assertion ((void *)0) != ptr occurred
+[ OK ] test_gf_realloc_ptr
+[==========] 10 test(s) run.
+[ PASSED ] 10 test(s).
+[ FAILED ] 0 test(s).
+[ REPORT ] Created libglusterfs_mem_pool_xunit.xml report
+```
+
+
+## Writing Unit Tests
+
+### Enhancing your C functions
+
+#### Programming by Contract
+Add the following to your C file:
+
+```c
+#include <cmockery/pbc.h>
+```
+
+```c
+/*
+ * Programming by Contract is a programming methodology
+ * which binds the caller and the function called to a
+ * contract. The contract is represented using Hoare Triple:
+ * {P} C {Q}
+ * where {P} is the precondition before executing command C,
+ * and {Q} is the postcondition.
+ *
+ * See also:
+ * http://en.wikipedia.org/wiki/Design_by_contract
+ * http://en.wikipedia.org/wiki/Hoare_logic
+ * http://dlang.org/dbc.html
+ */
+ #ifndef CMOCKERY_PBC_H_
+#define CMOCKERY_PBC_H_
+
+#if defined(UNIT_TESTING) || defined (DEBUG)
+
+#include <assert.h>
+
+/*
+ * Checks caller responsability against contract
+ */
+#define REQUIRE(cond) assert(cond)
+
+/*
+ * Checks function reponsability against contract.
+ */
+#define ENSURE(cond) assert(cond)
+
+/*
+ * While REQUIRE and ENSURE apply to functions, INVARIANT
+ * applies to classes/structs. It ensures that intances
+ * of the class/struct are consistant. In other words,
+ * that the instance has not been corrupted.
+ */
+#define INVARIANT(invariant_fnc) do{ (invariant_fnc) } while (0);
+
+#else
+#define REQUIRE(cond) do { } while (0);
+#define ENSURE(cond) do { } while (0);
+#define INVARIANT(invariant_fnc) do{ } while (0);
+
+#endif /* defined(UNIT_TESTING) || defined (DEBUG) */
+#endif /* CMOCKERY_PBC_H_ */
+```
+
+##### Example
+This is an _extremely_ simple example:
+
+```c
+int divide (int n, int d)
+{
+ int ans;
+
+ REQUIRE(d != 0);
+
+ ans = n / d;
+
+ // As code is added to this function throughout its lifetime,
+ // ENSURE will assert that data will be returned
+ // according to the contract. Again this is an
+ // extremely simple example. :-D
+ ENSURE( ans == (n / d) );
+
+ return ans;
+}
+
+```
+
+##### Important Note
+`REQUIRE`, `ENSURE`, and `INVARIANT` are only available when `DEBUG` or `UNIT_TESTING` are set in the CFLAGS. You must pass `--enable-debug` to `./configure` to enable PBC on your non-unittest builds.
+
+#### Overriding functions
+Cmockery2 provides its own memory allocation functions which check for buffer overrun and memory leaks. The following header file must be included **last** to be able to override any of the memory allocation functions:
+
+```c
+#include <cmockery/cmockery_override.h>
+```
+
+This file will only take effect with the `UNIT_TESTING` CFLAG is set.
+
+### Creating a unit test
+Once you identify the C file you would like to test, first create a `unittest` directory under the directory where the C file is located. This will isolate the unittests to a different directory.
+
+Next, you need to edit the `Makefile.am` file in the directory where your C file is located. Initialize the
+`Makefile.am` if it does not already have the following sections:
+
+```
+#### UNIT TESTS #####
+CLEANFILES += *.gcda *.gcno *_xunit.xml
+noinst_PROGRAMS =
+TESTS =
+```
+
+Now you can add the following for each of the unit tests that you would like to build:
+
+```
+### UNIT TEST xxx_unittest ###
+xxx_unittest_CPPFLAGS = $(UNITTEST_CPPFLAGS) $(xxx_CPPFLAGS)
+xxx_unittest_SOURCES = xxx.c \
+ unittest/xxx_unittest.c
+xxx_unittest_CFLAGS = $(UNITTEST_CFLAGS)
+xxx_unittest_LDADD = $(UNITTEST_LDADD)
+xxx_unittest_LDFLAGS = $(UNITTEST_LDFLAGS)
+noinst_PROGRAMS += xxx_unittest
+TESTS += xxx_unittest
+```
+
+Where `xxx` is the name of your C file. For example, look at `libglusterfs/src/Makefile.am`.
+
+Copy the simple unit test from `cmockery2/src/example/run_tests.c` to `unittest/xxx_unittest.c`. If you would like to see an example of a unit test, please refer to `libglusterfs/src/unittest/mem_pool_unittest.c`.
+
+#### Mocking
+You may see that the linker will complain about missing functions needed by the C file you would like to test. Identify the required functions, then place their stubs in a file called `unittest/xxx_mock.c`, then include this file in `Makefile.am` in `xxx_unittest_SOURCES`. This will allow you to you Cmockery2's mocking functions.
+
+#### Running the unit test
+You can type `make` in the directory where the C file is located. Once you built it and there are no errors, you can execute the test either by directly executing the program (in our example above it is called `xxx_unittest` ), or by running `make check`.
+
+#### Debugging
+Sometimes you may need to debug your unit test. To do that, you will have to point `gdb` to the actual binary which is located in the `.libs` subdirectory. For example, you can do the following from the root of the source tree to debug `mem_pool_unittest`:
+
+```
+$ export LD_LIBRARY_PATH=cmockery2/.libs
+$ gdb ./libglusterfs/src/.libs/mem_pool_unittest
+```
+
+
+[Cmockery2]: https://github.com/lpabon/cmockery2
+[definitionofunittest]: http://artofunittesting.com/definition-of-a-unit-test/
+[cmockery2usage]: https://github.com/lpabon/cmockery2/blob/master/doc/usage.md