Re: [PATCH/RFC] clk: gate: Add some kunit test suites

[Vaittinen, Matti]

Hello David, & All

This review and mail is more for pointing out the downsides of UTs. I
am not demanding any changes, these comments can be seen as 'nit's.

On Wed, 2020-04-29 at 12:15 +0800, David Gow wrote:
> On Tue, Apr 14, 2020 at 7:46 PM Vaittinen, Matti
> <Matti.Vaittinen@xxxxxxxxxxxxxxxxx> wrote:
> > Hello Stephen & All,
> > 
> > Prologue:
> > 
> > I have been traumatized in the past - by unit tests :) Thus I am
> > always
> > a bit jumpy when I see people adding UTs. I always see the inertia
> > UTs
> > add to development - when people change anything they must also
> > change
> > impacted UTs - and every unnecessary UT case is actually burden. I
> > was
> > once buried under such burden.. Back at those times I quite often
> > found
> > myself wondering why I spend two days fixing UT cases after I did a
> > necessary code change which took maybe 10 minutes. Please see my
> > comments knowing this history and do your decisions based on less
> > biased - brighter understanding :]
> > 
> > 
> 
> Hey Matti,
> 
> As someone who's definitely wasted a lot of time fixing
> poorly-thought-through tests, but who is nevertheless working
> enthusiastically on KUnit, I wanted to respond quickly here.

I appreciate your reply. And I appreciate your (and others) work on
KUinit. I don't think UTs are bad. I believe UTs are great and
powerfull tool - when used on specific occasions. But UTs definitely
are "double-edged sword" - you can hit your own leg.

> Certainly, the goal is not to reduce development velocity, though it
> is redistributed a bit: hopefully the extra time spent updating tests
> will be more than paid back in identifying and fixing bugs earlier,
> as
> well as making testing one's own changes simpler. Only time will tell
> if we're right or not, but if they turn out to cause more problems
> than they solve we can always adjust or remove them. I remain
> optimistic, though.

Fixing and identifying bugs is definitely "the thing" in UTs. But what
comes to weighing the benefits of UTs Vs. downsides - that's hard.
First thing on that front is to understand the cost of UTs. And in my
experience - many people underestimate that. It's easy too see things
black & white and think UTs are only good - which is not true.

UT cases are code which must be maintained as any code. And we must
never add code which is not beneficial as maintaining it is work. We do
constantly work to decrease amount of code to be maintaned - UTs are no
exception - all code is a burden. Unnecessary code is burden with no
purpose. And UTs have no other purpose but to point out mistakes. Only
good test is a test that is failing and pointing out a bug which would
have otherwise gone unnoticed. Passing test is a waste.

So key thing when considering if adding a test is beneficial is whether
the test is likely to point out a bug (in early phase). A bug that
would otherwise have gone through unnoticed.

> I do think that these tests are unlikely to increase the burden on
> developers much:

All code which uses kernel APIs is increasing burden for someone who
needs to change the API. Much can be discussed ;)

>  they seem mostly to test interfaces and behaviour
> which is used quite a bit elsewhere in the kernel: changes that break
> them seem likely to be reasonably disruptive anyway, so these tests
> aren't going to add too much to that overall,

This statement is valid for almost all exported kernel APIs - yet
adding tests for all APIs is definitely a bad idea. The effort is
cumulative. We should never add new code just because maintenance
effort is relatively small. We must only add code if it adds value.

>  and may ultimately make
> things a bit simpler by helping to document and verify the changes.

Yes. Definitely. But we must never deny that all added (test) code adds
work. And do weighing pros an cons only after that. Danger of UTs is
that we don't admit the cons.

> A few other notes inline:
> 
> > On Tue, 2020-04-07 at 20:56 -0700, Stephen Boyd wrote:
> > > Test various parts of the clk gate implementation with the kunit
> > > testing
> > > framework.
> > > 
> > > Cc: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
> > > Cc: <kunit-dev@xxxxxxxxxxxxxxxx>
> > > Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxx>
> > > ---
> > > 
> > > This patch is on top of this series[1] that allows the clk
> > > framework to be selected by Kconfig language.
> > > 
> > > [1]
> > > https://lore.kernel.org/r/20200405025123.154688-1-sboyd@xxxxxxxxxx
> > > 
> > >  drivers/clk/Kconfig         |   8 +
> > >  drivers/clk/Makefile        |   1 +
> > >  drivers/clk/clk-gate-test.c | 481
> > > ++++++++++++++++++++++++++++++++++++
> > >  3 files changed, 490 insertions(+)
> > >  create mode 100644 drivers/clk/clk-gate-test.c
> > > 
> > > diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
> > > index 6ea0631e3956..66193673bcdf 100644
> > > --- a/drivers/clk/Kconfig
> > > +++ b/drivers/clk/Kconfig
> > > @@ -377,4 +377,12 @@ source "drivers/clk/ti/Kconfig"
> > >  source "drivers/clk/uniphier/Kconfig"
> > >  source "drivers/clk/zynqmp/Kconfig"
> > > 
> > > +# Kunit test cases
> > > +config CLK_GATE_TEST
> > > +     tristate "Basic gate type Kunit test"
> > > +     depends on KUNIT
> > > +     default KUNIT
> > > +     help
> > > +       Kunit test for the basic clk gate type.
> > > +
> > >  endif
> > > diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile
> > > index f4169cc2fd31..0785092880fd 100644
> > > --- a/drivers/clk/Makefile
> > > +++ b/drivers/clk/Makefile
> > > @@ -7,6 +7,7 @@ obj-$(CONFIG_COMMON_CLK)      += clk-divider.o
> > >  obj-$(CONFIG_COMMON_CLK)     += clk-fixed-factor.o
> > >  obj-$(CONFIG_COMMON_CLK)     += clk-fixed-rate.o
> > >  obj-$(CONFIG_COMMON_CLK)     += clk-gate.o
> > > +obj-$(CONFIG_CLK_GATE_TEST)  += clk-gate-test.o
> > >  obj-$(CONFIG_COMMON_CLK)     += clk-multiplier.o
> > >  obj-$(CONFIG_COMMON_CLK)     += clk-mux.o
> > >  obj-$(CONFIG_COMMON_CLK)     += clk-composite.o
> > > diff --git a/drivers/clk/clk-gate-test.c b/drivers/clk/clk-gate-
> > > test.c
> > > new file mode 100644
> > > index 000000000000..b1d6c21e9698
> > > --- /dev/null
> > > +++ b/drivers/clk/clk-gate-test.c
> > > @@ -0,0 +1,481 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * KUnit test for clk gate basic type
> > > + */
> > > +#include <linux/clk.h>
> > > +#include <linux/clk-provider.h>
> > > +#include <linux/platform_device.h>
> > > +
> > > +#include <kunit/test.h>
> > > +
> > > +static void clk_gate_register_test_dev(struct kunit *test)
> > > +{
> > > +     struct clk_hw *ret;
> > > +     struct platform_device *pdev;
> > > +
> > > +     pdev = platform_device_register_simple("test_gate_device",
> > > -1,
> > > NULL, 0);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, pdev);
> > > +
> > > +     ret = clk_hw_register_gate(&pdev->dev, "test_gate", NULL,
> > > 0,
> > > NULL,
> > > +                                0, 0, NULL);
> > > +     KUNIT_EXPECT_NOT_ERR_OR_NULL(test, ret);
> > > +     KUNIT_EXPECT_STREQ(test, "test_gate",
> > > clk_hw_get_name(ret));
> > > +     KUNIT_EXPECT_EQ(test, 0UL, clk_hw_get_flags(ret));
> > > +
> > > +     clk_hw_unregister_gate(ret);
> > > +     platform_device_put(pdev);
> > > +}
> > > +
> > > +static void clk_gate_register_test_parent_names(struct kunit
> > > *test)
> > > +{
> > > +     struct clk_hw *parent;
> > > +     struct clk_hw *ret;
> > > +
> > > +     parent = clk_hw_register_fixed_rate(NULL, "test_parent",
> > > NULL,
> > > 0,
> > > +                                         1000000);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, parent);
> > > +
> > > +     ret = clk_hw_register_gate(NULL, "test_gate",
> > > "test_parent", 0,
> > > NULL,
> > > +                                0, 0, NULL);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
> > > +     KUNIT_EXPECT_PTR_EQ(test, parent, clk_hw_get_parent(ret));
> > > +
> > > +     clk_hw_unregister_gate(ret);
> > > +     clk_hw_unregister_fixed_rate(parent);
> > > +}
> > > +
> > > +static void clk_gate_register_test_parent_data(struct kunit
> > > *test)
> > > +{
> > > +     struct clk_hw *parent;
> > > +     struct clk_hw *ret;
> > > +     struct clk_parent_data pdata = { };
> > > +
> > > +     parent = clk_hw_register_fixed_rate(NULL, "test_parent",
> > > NULL,
> > > 0,
> > > +                                         1000000);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, parent);
> > > +     pdata.hw = parent;
> > > +
> > > +     ret = clk_hw_register_gate_parent_data(NULL, "test_gate",
> > > &pdata, 0,
> > > +                                            NULL, 0, 0, NULL);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
> > > +     KUNIT_EXPECT_PTR_EQ(test, parent, clk_hw_get_parent(ret));
> > > +
> > > +     clk_hw_unregister_gate(ret);
> > > +     clk_hw_unregister_fixed_rate(parent);
> > > +}
> > > +
> > > +static void clk_gate_register_test_parent_data_legacy(struct
> > > kunit
> > > *test)
> > > +{
> > > +     struct clk_hw *parent;
> > > +     struct clk_hw *ret;
> > > +     struct clk_parent_data pdata = { };
> > > +
> > > +     parent = clk_hw_register_fixed_rate(NULL, "test_parent",
> > > NULL,
> > > 0,
> > > +                                         1000000);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, parent);
> > > +     pdata.name = "test_parent";
> > > +
> > > +     ret = clk_hw_register_gate_parent_data(NULL, "test_gate",
> > > &pdata, 0,
> > > +                                            NULL, 0, 0, NULL);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
> > > +     KUNIT_EXPECT_PTR_EQ(test, parent, clk_hw_get_parent(ret));
> > > +
> > > +     clk_hw_unregister_gate(ret);
> > > +     clk_hw_unregister_fixed_rate(parent);
> > > +}
> > > +
> > > +static void clk_gate_register_test_parent_hw(struct kunit *test)
> > > +{
> > > +     struct clk_hw *parent;
> > > +     struct clk_hw *ret;
> > > +
> > > +     parent = clk_hw_register_fixed_rate(NULL, "test_parent",
> > > NULL,
> > > 0,
> > > +                                         1000000);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, parent);
> > > +
> > > +     ret = clk_hw_register_gate_parent_hw(NULL, "test_gate",
> > > parent,
> > > 0, NULL,
> > > +                                          0, 0, NULL);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
> > > +     KUNIT_EXPECT_PTR_EQ(test, parent, clk_hw_get_parent(ret));
> > > +
> > > +     clk_hw_unregister_gate(ret);
> > > +     clk_hw_unregister_fixed_rate(parent);
> > > +}
> > > +
> > > +static void clk_gate_register_test_hiword_invalid(struct kunit
> > > *test)
> > > +{
> > > +     struct clk_hw *ret;
> > > +
> > > +     ret = clk_hw_register_gate(NULL, "test_gate", NULL, 0,
> > > NULL,
> > > +                                20, CLK_GATE_HIWORD_MASK, NULL);
> > > +
> > > +     KUNIT_EXPECT_TRUE(test, IS_ERR(ret));
> > > +}
> > 
> > Do we really need all these registration tests? I guess most of the
> > code path would be tested by just one of these - how much value we
> > add
> > by adding rest of the registration cases? (just wondering)
> > 
> 
> The advantage of having multiple tests here is that it's really
> obvious if just one of these function breaks: that's probably not
> enormously likely,

My point exactly.

>  but there's also not much of a cost to having them

And this is the other side of the equation. And I leave this estimation
to others - I just want to point out that imbalance in this equation is
what usually leads to writing excessive amounts of tests - which
eventually just hinders development with little or no benefits. But as
I said, I will leave this to smarter guys to evaluate. Just wanted to
point out that this should be considered :)

> â these test would run pretty quickly, and wouldn't be too expensive
> to change in the unlikely event that was necessary.
> 
> > > +
> > > +static struct kunit_case clk_gate_register_test_cases[] = {
> > > +     KUNIT_CASE(clk_gate_register_test_dev),
> > > +     KUNIT_CASE(clk_gate_register_test_parent_names),
> > > +     KUNIT_CASE(clk_gate_register_test_parent_data),
> > > +     KUNIT_CASE(clk_gate_register_test_parent_data_legacy),
> > > +     KUNIT_CASE(clk_gate_register_test_parent_hw),
> > > +     KUNIT_CASE(clk_gate_register_test_hiword_invalid),
> > > +     {}
> > > +};
> > > +
> > > +static struct kunit_suite clk_gate_register_test_suite = {
> > > +     .name = "clk-gate-register-test",
> > > +     .test_cases = clk_gate_register_test_cases,
> > > +};
> > > +
> > > +struct clk_gate_test_context {
> > > +     void __iomem *fake_mem;
> > > +     struct clk_hw *hw;
> > > +     struct clk_hw *parent;
> > > +     u32 fake_reg; /* Keep at end, KASAN can detect out of
> > > bounds */
> > > +};
> > > +
> > > +static struct clk_gate_test_context
> > > *clk_gate_test_alloc_ctx(struct
> > > kunit *test)
> > > +{
> > > +     struct clk_gate_test_context *ctx;
> > > +
> > > +     test->priv = ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
> > > +     ctx->fake_mem = (void __force __iomem *)&ctx->fake_reg;
> > > +
> > > +     return ctx;
> > > +}
> > > +
> > > +static void clk_gate_test_parent_rate(struct kunit *test)
> > > +{
> > > +     struct clk_gate_test_context *ctx = test->priv;
> > > +     struct clk_hw *parent = ctx->parent;
> > > +     struct clk_hw *hw = ctx->hw;
> > > +     unsigned long prate = clk_hw_get_rate(parent);
> > > +     unsigned long rate = clk_hw_get_rate(hw);
> > > +
> > > +     KUNIT_EXPECT_EQ(test, prate, rate);
> > > +}
> > > +
> > > +static void clk_gate_test_enable(struct kunit *test)
> > > +{
> > > +     struct clk_gate_test_context *ctx = test->priv;
> > > +     struct clk_hw *parent = ctx->parent;
> > > +     struct clk_hw *hw = ctx->hw;
> > > +     struct clk *clk = hw->clk;
> > > +     int ret;
> > > +     u32 enable_val = BIT(5);
> > > +
> > > +     ret = clk_prepare_enable(clk);
> > > +     KUNIT_ASSERT_EQ(test, ret, 0);
> > > +
> > > +     KUNIT_EXPECT_EQ(test, enable_val, ctx->fake_reg);
> > > +     KUNIT_EXPECT_TRUE(test, clk_hw_is_enabled(hw));
> > > +     KUNIT_EXPECT_TRUE(test, clk_hw_is_prepared(hw));
> > > +     KUNIT_EXPECT_TRUE(test, clk_hw_is_enabled(parent));
> > > +     KUNIT_EXPECT_TRUE(test, clk_hw_is_prepared(parent));
> > > +}
> > 
> > Is this really necessary? Wouldn't most of this be tested by
> > clk_gate_test_disable()?
> > 
> 
> While _enable and _disable are likely pretty similar, having both
> tests here would catch things like copy-paste bugs from one to the
> other, which is probably worth the extra test. Particularly given
> that
> basically all of the functions tested are actually different
> functions.

The disable test already does the enable. Just adding another set of
state checks before disable would verify whole thing, right? So, if I
am not mistaken then - by minimum - these could be tested at one go.
(If being beneficial at all).

> > > +
> > > +static void clk_gate_test_disable(struct kunit *test)
> > > +{
> > > +     struct clk_gate_test_context *ctx = test->priv;
> > > +     struct clk_hw *parent = ctx->parent;
> > > +     struct clk_hw *hw = ctx->hw;
> > > +     struct clk *clk = hw->clk;
> > > +     int ret;
> > > +     u32 enable_val = BIT(5);
> > > +     u32 disable_val = 0;
> > > +
> > > +     ret = clk_prepare_enable(clk);
> > > +     KUNIT_ASSERT_EQ(test, ret, 0);
> > > +     KUNIT_ASSERT_EQ(test, enable_val, ctx->fake_reg);
> > > +
> > > +     clk_disable_unprepare(clk);
> > > +     KUNIT_EXPECT_EQ(test, disable_val, ctx->fake_reg);
> > > +     KUNIT_EXPECT_FALSE(test, clk_hw_is_enabled(hw));
> > > +     KUNIT_EXPECT_FALSE(test, clk_hw_is_prepared(hw));
> > > +     KUNIT_EXPECT_FALSE(test, clk_hw_is_enabled(parent));
> > > +     KUNIT_EXPECT_FALSE(test, clk_hw_is_prepared(parent));
> > > +}
> > > +
> > > +static struct kunit_case clk_gate_test_cases[] = {
> > > +     KUNIT_CASE(clk_gate_test_parent_rate),
> > > +     KUNIT_CASE(clk_gate_test_enable),
> > > +     KUNIT_CASE(clk_gate_test_disable),
> > > +     {}
> > > +};
> > > +
> > > +static int clk_gate_test_init(struct kunit *test)
> > > +{
> > > +     struct clk_hw *parent;
> > > +     struct clk_hw *hw;
> > > +     struct clk_gate_test_context *ctx;
> > > +
> > > +     ctx = clk_gate_test_alloc_ctx(test);
> > > +     parent = clk_hw_register_fixed_rate(NULL, "test_parent",
> > > NULL,
> > > 0,
> > > +                                         2000000);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, parent);
> > > +
> > > +     hw = clk_hw_register_gate_parent_hw(NULL, "test_gate",
> > > parent,
> > > 0,
> > > +                                         ctx->fake_mem, 5, 0,
> > > NULL);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, hw);
> > > +
> > > +     ctx->hw = hw;
> > > +     ctx->parent = parent;
> > > +
> > > +     return 0;
> > > +}
> > > +
> > > +static void clk_gate_test_exit(struct kunit *test)
> > > +{
> > > +     struct clk_gate_test_context *ctx = test->priv;
> > > +
> > > +     clk_hw_unregister_gate(ctx->hw);
> > > +     clk_hw_unregister_fixed_rate(ctx->parent);
> > > +     kfree(ctx);
> > > +}
> > 
> > Aren't these init and exit actually covering some of the things
> > tested
> > in clk_gate_register_test_cases? Perhaps we could reduce some tests
> > or
> > use some test functions as init/exit?
> > 
> 
> Logically, these init/exit functions are not supposed to be testing
> anything in and of themselves, just setting up the environment for
> other tests.
> I do like the idea of reducing code duplication by, say, moving some
> of the code into a separate helper function. I'm a little wary of
> actually using the same function as an init function as a test: that
> seems more confusing than the duplication to me, but that's just
> personal preference, I think.
> 
> > > +
> > > +static struct kunit_suite clk_gate_test_suite = {
> > > +     .name = "clk-gate-test",
> > > +     .init = clk_gate_test_init,
> > > +     .exit = clk_gate_test_exit,
> > > +     .test_cases = clk_gate_test_cases,
> > > +};
> > > +
> > > +static void clk_gate_test_invert_enable(struct kunit *test)
> > > +{
> > > +     struct clk_gate_test_context *ctx = test->priv;
> > > +     struct clk_hw *parent = ctx->parent;
> > > +     struct clk_hw *hw = ctx->hw;
> > > +     struct clk *clk = hw->clk;
> > > +     int ret;
> > > +     u32 enable_val = 0;
> > > +
> > > +     ret = clk_prepare_enable(clk);
> > > +     KUNIT_ASSERT_EQ(test, ret, 0);
> > > +
> > > +     KUNIT_EXPECT_EQ(test, enable_val, ctx->fake_reg);
> > > +     KUNIT_EXPECT_TRUE(test, clk_hw_is_enabled(hw));
> > > +     KUNIT_EXPECT_TRUE(test, clk_hw_is_prepared(hw));
> > > +     KUNIT_EXPECT_TRUE(test, clk_hw_is_enabled(parent));
> > > +     KUNIT_EXPECT_TRUE(test, clk_hw_is_prepared(parent));
> > > +}
> > 
> > Is this really adding value after clk_gate_test_invert_disable()
> > has
> > passed?
> > 
> > +
> > > +static void clk_gate_test_invert_disable(struct kunit *test)
> > > +{
> > > +     struct clk_gate_test_context *ctx = test->priv;
> > > +     struct clk_hw *parent = ctx->parent;
> > > +     struct clk_hw *hw = ctx->hw;
> > > +     struct clk *clk = hw->clk;
> > > +     int ret;
> > > +     u32 enable_val = 0;
> > > +     u32 disable_val = BIT(15);
> > > +
> > > +     ret = clk_prepare_enable(clk);
> > > +     KUNIT_ASSERT_EQ(test, ret, 0);
> > > +     KUNIT_ASSERT_EQ(test, enable_val, ctx->fake_reg);
> > > +
> > > +     clk_disable_unprepare(clk);
> > > +     KUNIT_EXPECT_EQ(test, disable_val, ctx->fake_reg);
> > > +     KUNIT_EXPECT_FALSE(test, clk_hw_is_enabled(hw));
> > > +     KUNIT_EXPECT_FALSE(test, clk_hw_is_prepared(hw));
> > > +     KUNIT_EXPECT_FALSE(test, clk_hw_is_enabled(parent));
> > > +     KUNIT_EXPECT_FALSE(test, clk_hw_is_prepared(parent));
> > > +}
> > > +
> > > +static struct kunit_case clk_gate_test_invert_cases[] = {
> > > +     KUNIT_CASE(clk_gate_test_invert_enable),
> > > +     KUNIT_CASE(clk_gate_test_invert_disable),
> > > +     {}
> > > +};
> > > +
> > > +static int clk_gate_test_invert_init(struct kunit *test)
> > > +{
> > > +     struct clk_hw *parent;
> > > +     struct clk_hw *hw;
> > > +     struct clk_gate_test_context *ctx;
> > > +
> > > +     ctx = clk_gate_test_alloc_ctx(test);
> > > +     parent = clk_hw_register_fixed_rate(NULL, "test_parent",
> > > NULL,
> > > 0,
> > > +                                         2000000);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, parent);
> > > +
> > > +     ctx->fake_reg = BIT(15); /* Default to off */
> > > +     hw = clk_hw_register_gate_parent_hw(NULL, "test_gate",
> > > parent,
> > > 0,
> > > +                                         ctx->fake_mem, 15,
> > > +                                         CLK_GATE_SET_TO_DISABLE
> > > ,
> > > NULL);
> > > +     KUNIT_ASSERT_NOT_ERR_OR_NULL(test, hw);
> > > +
> > > +     ctx->hw = hw;
> > > +     ctx->parent = parent;
> > > +
> > > +     return 0;
> > > +}
> > 
> > Aren't these init and exit actually covering some of the things
> > tested
> > in clk_gate_register_test_cases? Perhaps we could reduce some tests
> > or
> > use some test functions as init/exit?
> 
> As above, I personally like having the test versions as well, as it
> ensures that there's at least one test showing the failure in its
> actual test function. But reusing the actual code wouldn't be a
> problem, and is probably just a matter of taste.
> 
> > I stopped reviewing here - I think you know what I was up-to and
> > you
> > are the best experts to evaluate whether there is something to
> > squash/drop also in the rest of the tests :)
> > 
> > 
> > Epilogue:
> > 
> > In general, I would be very careful when adding UT-code and I would
> > try
> > to minimize the required test changes when for example one of the
> > clk
> > APIs require a change. (I know, the test changes are least thing to
> > worry if these APIs need change - but effort is still cumulative
> > and if
> > we can avoid some - we should).
> > 
> > I don't mean to be disrespectful. I know my place in the food-chain 
> > :p
> > Besides, I have seen the great work Stephen has been doing with clk
> > -
> > and I believe he knows what he is doing. But sometimes little
> > poking
> > can invoke new thoughts :grin: You can ignore my comments if they
> > make
> > no sense to you.
> > 
> > Best Regards
> >   --Matti
> 
> While I obviously sit more on the "yes" side of the unit-testing
> fence, you've definitely raised some interesting points. Personally,
> I'd really like to see this test go in (whether as-is, or with minor
> adjustments), but writing up a KUnit "testing style guide" or similar
> is on my to-do list, and I'm definitely going to want to think more
> about how best to handle some of these situations (and better
> articulate why).

I think this was more of my point than trying to demand actual changes
here. Thank you for considering this! :) It is important to admit that
_all_ code, whether test or implementation, require work and
maintenance and slow down development. We should _always_ consider if
adding a test is actually needed or if we could do it so that code
change require less test changes.

If I had all the power in the world I would never add a test for code
which is clean and simple. It is likely to not be beneficial. I would
mostly utilize UTs at spots where the logic is somewhat complex and
making a bug is likely. UTs do great job for example at verifying data
parsing functions (I've voluntarily tested bunch of netlink message
parsing code with UTs in some projects. I also added tests for
linear_ranges helpers in series I recently submitted.) But UTs are more
of a waste when added carelessly. I hope the UT documentation would
also cover that front.

Thanks for open discussion!

Yours,
--Matti