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