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The uptime mock example
=======================
This is a very simple example to explain the mocking feature of cmocka. It
implement the 'uptime' unix command in a very simple way to demonstrate how to
test the time calculation.
The problem with testing the uptime command is that /proc/uptime constantly
ticks. The result is random whenever you call the test. To actually test it
we need to make sure that we work with fixed values. The mocking features
of cmocka allows us to test it anyway!
Source files
------------
* *proc_uptime.c*: This implements the `uptime()` function reading and parsing
the /proc/uptime file.
* *uptime.c*: This is the actual uptime implementation, it calls
`calc_uptime()` to get a human readable string representation of the uptime.
This function calls `uptime()` from proc_uptime.c.
* *test_uptime.c*: This is the test with the mocking function for uptime().
Linking magic
-------------
The test is linked using:
ld --wrap=uptime
This replaces the orginal `uptime()` function which reads from `/proc/uptime`
with the mock function we implemented for testing `calc_uptime()`.
The mock function we implemented has a special name. It is called
`__wrap_uptime()`. All the symbols you want to mock (or replace) need to start
with the prefix `__wrap_`. So `ld --wrap=uptime` will rename the orignal
`uptime()` function to `__real_uptime()`. This means you can still reach the
original function using that name and call it e.g. from the wrap function.
The symbol `uptime` will be bound to `__wrap_uptime`.
You can find more details in the manpage: `man ld`
The uptime test
---------------
The code should be easy to understand. If you have a hard time following, there
are two ways to understand how things work.
You can find out details about symbol binding using:
LD_DEBUG=symbols ./example/uptime/uptime
LD_DEBUG=symbols ./example/uptime/test_uptime
You can also use a debugger to step through the code!
Have fun!
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