5. KTF Basic Concepts

Tests and test suites

The simplest form of test is to just specify:

TEST(suite_name, test_name)
        <test code and assertions go here>

A KTF test is declared with TEST() or TEST_F(), which both takes both a test suite name and a test name, which are two different name spaces. Consequently, each test belongs to one test suite, and the test suites are created based on what tests that exists. A test suite is just a container of tests which in user space contributes to the extended name of a test. Test names must be unique within a suite, and test names must also be unique within a source file, since the test name is the only parameter needed when adding a test.

All tests must be added using ADD_TEST or ADD_LOOP_TEST to be visible to KTF's runtime framework. This allows tests to be declared while under development, but not added (or the ADD_TEST could be commented out) if the test or the kernel module under test is not ready yet for some reason.

Test fixtures

As in other unit test frameworks, a test fixture is a mechanism to allow several tests to run under the same conditions, in that setup and teardown is done before and after each test. In KTF a test fixture must first be declared with DECLARE_F() which takes a fixture name followed by a list of attributes and an end brace, and initialized with INIT_F() which takes the fixture name and a setup and teardown function to be defined subsequently. Note that there are no start brace, which is intentional:

        int value;
        struct my_details;
INIT_F(a_fixture, a_setup, a_teardown);

Then to the implementation of the fixture, in the form of actual setup and a teardown functions that may operate on the attributes of the fixture:

SETUP_F(a_fixture, a_setup)
        a_fixture->value = 42; /* or whatever.. */
        <other actions needed to set up>
        /* If everything went well during setup: */
        a_fixture->ok = true;

TEARDOWN_F(a_fixture, a_teardown)
        <necessary cleanup code>

Now individual tests that uses this fixture can be declared with:

TEST_F(a_fixture, suite_name, test_name)
        <test code>


A context provides a way to instantiate a test in multiple ways. A typical use case is if you have multiple similar devices you want to run a set of tests on. Another use case could be that you want to run a set of tests under different configurations.

You are free to let the number and names of these contexts vary as to where you run your test. For the devices use case, you can have the init function loop through all available devices, to identify the ones the tests applies to, then instantiate a context for each device, possibly using the device name for trackability. The context names will be prepended to the test name and the number of available tests will be multipled by the number of contexts.

Note that the state of a context persists through the whole "life" of the module (until it gets unloaded) so it can be used to store more long term bookeeping in addition to any configuration information. The test writer must make sure that subsequent runs of the test suite (or parallel runs!) does not interfere with each other. Similar to fixtures, there's a generic part that KTF uses, and it can be extended the normal way. Make sure to declare the test specific context struct type with an element named:

struct ktf_context k;

typically as the first element of the struct, then you can continue with whatever other datastructure desired. A test module can declare and use as many contexts as desired. Note that contexts are associated with and unique within a handle (see below). So if you need to use a different set of contexts for different tests, you need to put these contexts and tests into different handles.

A context can be added using something like:

KTF_CONTEXT_ADD(&my_struct.k, "mycfg")

where the first argument is a reference to the ktf_context structure within the test specific structure, and the second argument is a text name to use to refer to the context. Once one or more contexts exists for a handle, tests for that handle will show up with names postfixed by the context name, and there will be a distinct version of the test for each context, e.g if a handle has contexts named c1 and c2, and tests declared with TEST(x, t1) and TEST(x, t2), then this will manifest as 4 tests:


Tests that depends on having a context

It is likely that once you have a set of tests that uses contexts, that they also depends on a context being available, e.g. that the ctx variable inside a test points to a non-nil context. One example use case for contexts would be a certain class of device. Such a device might or might not be available in the system. If one or more devices are available, you might want to have tests named c.t1_dev1 and c.t1_dev2 where dev1 and dev2 are the device names for these devices in the system, but never have any c.t1 test without a device. You can enforce this by letting tests associated with a handle requiring a context to even show up as a test in the list or be available for execution. Instead of using KTF_INIT() or KTF_HANDLE_INIT(), use KTF_CTX_INIT() or KTF_HANDLE_CTX_INIT().

Configurable contexts

Sometimes it might be useful to be able to configure a context for the execution of some (or all) of the tests using the context. This can be because the system the tests are running on might have different hardware or software capabilities, or might rely on differing device or network setup or naming. Typically we want a unit test suite to have as little configuration and parameterization as possible, so recommended use is for parameters that is not directly related to the operation of the test, but more for situations where parameters outside the test itself needs to be set up, such as connect details for a network service to test against, or a peer unit test process for network related tests that require more than one system to run. To specify a configurable context, use:

int my_cfg_callback(struct ktf_context *ctx, const void* data, size_t data_sz);

KTF_CONTEXT_ADD_CFG(&my_struct.k, "mycfg", my_cfg_callback, type_id)

The data pointer (and it's length) should be provided from user space, and it is up to the test specific user space and kernel space code to decide with the configuration is all about. If 0 is returned, KTF considers the context to be configured, otherwise it will retain it's current state, which will initially be unconfigured. The callback return value is stored as an errno value in ktf_context in the variable config_errno, which will initially be set to ENOENT, to indicate unconfigured. The test can use this value to decide what to do, such as failing with a message about missing configuration or just silently pass and ignore the case if not configured. The type_id parameter is used as a unique identifier for the kernel side to decide how to interpret the parameter, which is useful if different contexts wants to implement very different configuration options. It also allows two different test modules to use the same context names but with different parameters by using different context types.

In the user space part of the test, configuration information can be set for a context using:

KTF_CONTEXT_CFG(name, type_id, parameter_type, parameter_ref)

A simple example of a configurable test can be seen in the selftests test in selftest/context.c (kernel part) and user/context.cpp (user part) and the header file selftest/context_self.h shared between user space and kernel space.

Context types and user space created contexts

Contexts belong to a context type, which is a mechanism to group contexts into types that have similar properties. It is up to the kernel test module using these contexts what the meaning of this is, but a simple semantics can be that all contexts of a certain type has the same parameter block and the type ID can be used to check what type of context it is before trying to resolve or verify the parameters. For contexts pre-created by the kernel module, type IDs can be freely selected and does not have any further meaning beyond this.

Context types can however also be used to selectively allow user space to dynamically create new contexts of a specific type. To enable such functionality, the kernel test module will need to enable it for one or more context types. This is done by means of the following call:

ktf_handle_add_ctx_type(struct ktf_handle *handle,
                        struct ktf_context_type *type)

kernel side call, which tells KTF that a new context type with a given type ID permits user applications to create new contexts. This is useful for instance if user parameters or other information most easily obtainable from user land at test runtime is most easily available from user space.


Unlike user land unit test frameworks, which can rely on everything being cleaned up when the test program finished, KTF and test writers must pay the normal kernel level attention to allocations, references and deallocations.

KTF itself uses the concept of a handle to track tests, test suites and contexts associated with a kernel module. Contexts are also associated with a handle. Since the availability of contexts for a handle determines the availability of tests and the naming of them, it can be useful to have separate spaces for tests that relies on some context and tests that do not, to avoid aggregating up multiple test cases that are identical. Handles thus also have a namespace effect in that it is possible to have two contexts with the same name, and possibly a different type, by putting them in different handles.

The simplest mode of usage is for each module to use KTF_INIT() and KTF_CLEANUP() in it's __init and __exit functions. KTF_INIT implicitly declares and initializes a global handle __test_handle that gets cleaned up again in KTF_CLEANUP, making the handle something a test developer does not need to think too much about. However, sometimes a KTF kernel module may be such organized that it makes sense to use more than one handle. KTF allows the creation/cleanup of explicitly named handles by means of KTF_HANDLE_INIT(name) and KTF_HANDLE_CLEANUP(name). This can be used as an alternative to KTF_INIT()/KTF_CLEANUP() but requires the use of ADD_TEST_TO(handle, testname) instead of the normal ADD_TEST(testname) for adding tests to be executed.