- An assertion establishes truth (i.e. boolean True) for a single condition. Upon boolean False, an assertion stops execution and reports the failure.
- Unity is mainly a rich collection of assertions and the support to gather up and easily execute those assertions.
- The structure of Unity allows you to easily separate test assertions from source code in, well, test code.
- Unity’s assertions:
- Come in many, many flavors to handle different C types and assertion cases.
- Use context to provide detailed and helpful failure messages.
- Document types, expected values, and basic behavior in your source code for free.
One way to think of Unity is simply as a rich collection of assertions you can use to establish whether your source code behaves the way you think it does. Unity provides a framework to easily organize and execute those assertions in test code separate from your source code.
At their core, assertions are an establishment of truth - boolean truth. Was this thing equal to that thing? Does that code doohickey have such-and-such property or not? You get the idea. Assertions are executable code. Static analysis is a valuable approach to improving code quality, but it is not executing your code in the way an assertion can. A failing assertion stops execution and reports an error through some appropriate I/O channel (e.g. stdout, GUI, output file, blinky light).
Fundamentally, for dynamic verification all you need is a single assertion
mechanism. In fact, that’s what the assert() macro in C’s standard library
is for. So why not just use it? Well, we can do far better in the reporting
department. C’s assert() is pretty dumb as-is and is particularly poor for
handling common data types like arrays, structs, etc. And, without some other
support, it’s far too tempting to litter source code with C’s assert()’s. It’s
generally much cleaner, manageable, and more useful to separate test and source
code in the way Unity facilitates.
Asserting a simple truth condition is valuable, but using the context of the assertion is even more valuable. For instance, if you know you’re comparing bit flags and not just integers, then why not use that context to give explicit, readable, bit-level feedback when an assertion fails?
That’s what Unity’s collection of assertions do - capture context to give you helpful, meaningful assertion failure messages. In fact, the assertions themselves also serve as executable documentation about types and values in your source code. So long as your tests remain current with your source and all those tests pass, you have a detailed, up-to-date view of the intent and mechanisms in your source code. And due to a wondrous mystery, well-tested code usually tends to be well designed code.
The convention of assertion parameters generally follows this order:
TEST_ASSERT_X( {modifiers}, {expected}, actual, {size/count} )The very simplest assertion possible uses only a single actual parameter (e.g.
a simple null check).
Actualis the value being tested and unlike the other parameters in an assertion construction is the only parameter present in all assertion variants.Modifiersare masks, ranges, bit flag specifiers, floating point deltas.Expectedis your expected value (duh) to compare to anactualvalue; it’s marked as an optional parameter because some assertions only need a singleactualparameter (e.g. null check).Size/countrefers to string lengths, number of array elements, etc.
Many of Unity’s assertions are clear duplications in that the same data type
is handled by several assertions. The differences among these are in how failure
messages are presented. For instance, a _HEX variant of an assertion prints
the expected and actual values of that assertion formatted as hexadecimal.
All assertions are complemented with a variant that includes a simple string message as a final parameter. The string you specify is appended to an assertion failure message in Unity output.
For brevity, the assertion variants with a message parameter are not listed
below. Just tack on _MESSAGE as the final component to any assertion name in
the reference list below and add a string as the final parameter.
Example:
TEST_ASSERT_X( {modifiers}, {expected}, actual, {size/count} )becomes messageified like thus…
TEST_ASSERT_X_MESSAGE( {modifiers}, {expected}, actual, {size/count}, message )Notes:
- The
_MESSAGEvariants intentionally do not supportprintfstyle formatting since many embedded projects don’t support or avoidprintffor various reasons. It is possible to usesprintfbefore the assertion to assemble a complex fail message, if necessary. - If you want to output a counter value within an assertion fail message (e.g. from
a loop) , building up an array of results and then using one of the
_ARRAYassertions (see below) might be a handy alternative tosprintf.
Unity provides a collection of assertions for arrays containing a variety of
types. These are documented in the Array section below. These are almost on par
with the _MESSAGEvariants of Unity’s Asserts in that for pretty much any Unity
type assertion you can tack on _ARRAY and run assertions on an entire block of
memory.
TEST_ASSERT_EQUAL_TYPEX_ARRAY( expected, actual, {size/count} )Expectedis an array itself.Size/countis one or two parameters necessary to establish the number of array elements and perhaps the length of elements within the array.
Notes:
- The
_MESSAGEvariant convention still applies here to array assertions. The_MESSAGEvariants of the_ARRAYassertions have names ending with_ARRAY_MESSAGE. - Assertions for handling arrays of floating point values are grouped with float and double assertions (see immediately following section).
Unity provides a collection of assertions for arrays containing a variety of
types which can be compared to a single value as well. These are documented in
the Each Equal section below. these are almost on par with the _MESSAGE
variants of Unity’s Asserts in that for pretty much any Unity type assertion you
can inject _EACH_EQUAL and run assertions on an entire block of memory.
TEST_ASSERT_EACH_EQUAL_TYPEX( expected, actual, {size/count} )Expectedis a single value to compare to.Actualis an array where each element will be compared to the expected value.Size/countis one of two parameters necessary to establish the number of array elements and perhaps the length of elements within the array.
Notes:
- The
_MESSAGEvariant convention still applies here to Each Equal assertions. - Assertions for handling Each Equal of floating point values are grouped with float and double assertions (see immediately following section).
Support for floating point types is configurable. That is, by defining the appropriate preprocessor symbols, floats and doubles can be individually enabled or disabled in Unity code. This is useful for embedded targets with no floating point math support (i.e. Unity compiles free of errors for fixed point only platforms). See Unity documentation for specifics.
Not all targets support 64 bit wide types or even 32 bit wide types. Define the appropriate preprocessor symbols and Unity will omit all operations from compilation that exceed the maximum width of your target. See Unity documentation for specifics.
This fella is most often used in special conditions where your test code is
performing logic beyond a simple assertion. That is, in practice, TEST_FAIL()
will always be found inside a conditional code block.
Examples:
- Executing a state machine multiple times that increments a counter your test code then verifies as a final step.
- Triggering an exception and verifying it (as in Try / Catch / Throw - see the CException project).
This will abort the remainder of the test, but count the test as a pass. Under
normal circumstances, it is not necessary to include this macro in your tests…
a lack of failure will automatically be counted as a PASS. It is occasionally
useful for tests with #ifdefs and such.
Marks a test case (i.e. function meant to contain test assertions) as ignored. Usually this is employed as a breadcrumb to come back and implement a test case. An ignored test case has effects if other assertions are in the enclosing test case (see Unity documentation for more).
This can be useful for outputting INFO messages into the Unity output stream
without actually ending the test. Like pass and fail messages, it will be output
with the filename and line number.
A simple wording variation on TEST_ASSERT_FALSE.The semantics of
TEST_ASSERT_UNLESS aid readability in certain test constructions or
conditional statements.
Verify if a pointer is or is not NULL.
Verify if the first element dereferenced from a pointer is or is not zero. This is particularly useful for checking for empty (or non-empty) null-terminated C strings, but can be just as easily used for other null-terminated arrays.
Large integer sizes can be disabled for build targets that do not support them. For example, if your target only supports up to 16 bit types, by defining the appropriate symbols Unity can be configured to omit 32 and 64 bit operations that would break compilation (see Unity documentation for more). Refer to Advanced Asserting later in this document for advice on dealing with other word sizes.
All _HEX assertions are identical in function to unsigned integer assertions
but produce failure messages with the expected and actual values formatted
in hexadecimal. Unity output is big endian.
While you can use the 8-bit integer assertions to compare char, another option is
to use this specialized assertion which will show printable characters as printables,
otherwise showing the HEX escape code for the characters.
Masked and bit-level assertions produce output formatted in hexadecimal. Unity output is big endian.
Only compares the masked (i.e. high) bits of expected and actual parameters.
Asserts the masked bits of the actual parameter are high.
Asserts the masked bits of the actual parameter are low.
Asserts the specified bit of the actual parameter is high.
Asserts the specified bit of the actual parameter is low.
These assertions verify that the actual parameter is less than or greater
than threshold (exclusive). For example, if the threshold value is 0 for the
greater than assertion will fail if it is 0 or less. There are assertions for
all the various sizes of ints, as for the equality assertions. Some examples:
These assertions verify that the expected parameter is within +/- delta
(inclusive) of the actual parameter. For example, if the expected value is 10
and the delta is 3 then the assertion will fail for any value outside the range
of 7 - 13.
Asserts that the pointers point to the same memory location.
Asserts that the null terminated (’\0’)strings are identical. If strings are
of different lengths or any portion of the strings before their terminators
differ, the assertion fails. Two NULL strings (i.e. zero length) are considered
equivalent.
Asserts that the contents of the memory specified by the expected and actual
pointers is identical. The size of the memory blocks in bytes is specified by
the len parameter.
expected and actual parameters are both arrays. num_elements specifies the
number of elements in the arrays to compare.
_HEX assertions produce failure messages with expected and actual array
contents formatted in hexadecimal.
For array of strings comparison behavior, see comments for
TEST_ASSERT_EQUAL_STRING in the preceding section.
Assertions fail upon the first element in the compared arrays found not to match. Failure messages specify the array index of the failed comparison.
len is the memory in bytes to be compared at each array element.
These assertions verify that the expected array parameter is within +/- delta
(inclusive) of the actual array parameter. For example, if the expected value is
[10, 12] and the delta is 3 then the assertion will fail for any value
outside the range of [7 - 13, 9 - 15].
expected are single values and actual are arrays. num_elements specifies
the number of elements in the arrays to compare.
_HEX assertions produce failure messages with expected and actual array
contents formatted in hexadecimal.
Assertions fail upon the first element in the compared arrays found not to match. Failure messages specify the array index of the failed comparison.
len is the memory in bytes to be compared at each array element.
Asserts that the actual value is within +/- delta of the expected value.
The nature of floating point representation is such that exact evaluations of
equality are not guaranteed.
Asserts that the actual value is NOT within +/- delta of the expected value.
Asserts that the actual value is “close enough to be considered equal” to the
expected value. If you are curious about the details, refer to the Advanced
Asserting section for more details on this. Omitting a user-specified delta in a
floating point assertion is both a shorthand convenience and a requirement of
code generation conventions for CMock.
Asserts that the actual value is NOT “close enough to be considered equal” to the
expected value.
See Array assertion section for details. Note that individual array element
uses user-provided delta plus default comparison delta for checking
and is based on TEST_ASSERT_FLOAT_WITHIN comparison.
See Array assertion section for details. Note that individual array element
float comparisons are executed using TEST_ASSERT_EQUAL_FLOAT. That is, user
specified delta comparison values requires a custom-implemented floating point
array assertion.
Asserts that the actual parameter is less than threshold (exclusive).
For example, if the threshold value is 1.0f, the assertion will fail if it is
greater than 1.0f.
Asserts that the actual parameter is greater than threshold (exclusive).
For example, if the threshold value is 1.0f, the assertion will fail if it is
less than 1.0f.
Asserts that the actual parameter is less than or equal to threshold.
The rules for equality are the same as for TEST_ASSERT_EQUAL_FLOAT.
Asserts that the actual parameter is greater than threshold.
The rules for equality are the same as for TEST_ASSERT_EQUAL_FLOAT.
Asserts that actual parameter is equivalent to positive infinity floating
point representation.
Asserts that actual parameter is equivalent to negative infinity floating
point representation.
Asserts that actual parameter is a Not A Number floating point representation.
Asserts that actual parameter is a floating point representation usable for
mathematical operations. That is, the actual parameter is neither positive
infinity nor negative infinity nor Not A Number floating point representations.
Asserts that actual parameter is a value other than positive infinity floating
point representation.
Asserts that actual parameter is a value other than negative infinity floating
point representation.
Asserts that actual parameter is a value other than Not A Number floating
point representation.
Asserts that actual parameter is not usable for mathematical operations. That
is, the actual parameter is either positive infinity or negative infinity or
Not A Number floating point representations.
Asserts that the actual value is within +/- delta of the expected value.
The nature of floating point representation is such that exact evaluations of
equality are not guaranteed.
Asserts that the actual value is NOT within +/- delta of the expected value.
Asserts that the actual value is “close enough to be considered equal” to the
expected value. If you are curious about the details, refer to the Advanced
Asserting section for more details. Omitting a user-specified delta in a
floating point assertion is both a shorthand convenience and a requirement of
code generation conventions for CMock.
Asserts that the actual value is NOT “close enough to be considered equal” to the
expected value.
See Array assertion section for details. Note that individual array element
uses user-provided delta plus default comparison delta for checking
and is based on TEST_ASSERT_DOUBLE_WITHIN comparison.
See Array assertion section for details. Note that individual array element
double comparisons are executed using TEST_ASSERT_EQUAL_DOUBLE. That is, user
specified delta comparison values requires a custom implemented double array
assertion.
Asserts that the actual parameter is less than threshold (exclusive).
For example, if the threshold value is 1.0, the assertion will fail if it is
greater than 1.0.
Asserts that the actual parameter is less than or equal to threshold.
The rules for equality are the same as for TEST_ASSERT_EQUAL_DOUBLE.
Asserts that the actual parameter is greater than threshold (exclusive).
For example, if the threshold value is 1.0, the assertion will fail if it is
less than 1.0.
Asserts that the actual parameter is greater than or equal to threshold.
The rules for equality are the same as for TEST_ASSERT_EQUAL_DOUBLE.
Asserts that actual parameter is equivalent to positive infinity floating
point representation.
Asserts that actual parameter is equivalent to negative infinity floating point
representation.
Asserts that actual parameter is a Not A Number floating point representation.
Asserts that actual parameter is a floating point representation usable for
mathematical operations. That is, the actual parameter is neither positive
infinity nor negative infinity nor Not A Number floating point representations.
Asserts that actual parameter is a value other than positive infinity floating
point representation.
Asserts that actual parameter is a value other than negative infinity floating
point representation.
Asserts that actual parameter is a value other than Not A Number floating
point representation.
Asserts that actual parameter is not usable for mathematical operations. That
is, the actual parameter is either positive infinity or negative infinity or
Not A Number floating point representations.
This section helps you understand how to deal with some of the trickier assertion situations you may run into. It will give you a glimpse into some of the under-the-hood details of Unity’s assertion mechanisms. If you’re one of those people who likes to know what is going on in the background, read on. If not, feel free to ignore the rest of this document until you need it.
As you may know, directly checking for equality between a pair of floats or a pair of doubles is sloppy at best and an outright no-no at worst. Floating point values can often be represented in multiple ways, particularly after a series of operations on a value. Initializing a variable to the value of 2.0 is likely to result in a floating point representation of 2 x 20,but a series of mathematical operations might result in a representation of 8 x 2-2 that also evaluates to a value of 2. At some point repeated operations cause equality checks to fail.
So Unity doesn’t do direct floating point comparisons for equality. Instead, it
checks if two floating point values are “really close.” If you leave Unity
running with defaults, “really close” means “within a significant bit or two.”
Under the hood, TEST_ASSERT_EQUAL_FLOAT is really TEST_ASSERT_FLOAT_WITHIN
with the delta parameter calculated on the fly. For single precision, delta is
the expected value multiplied by 0.00001, producing a very small proportional
range around the expected value.
If you are expecting a value of 20,000.0 the delta is calculated to be 0.2. So any value between 19,999.8 and 20,000.2 will satisfy the equality check. This works out to be roughly a single bit of range for a single-precision number, and that’s just about as tight a tolerance as you can reasonably get from a floating point value.
So what happens when it’s zero? Zero - even more than other floating point values - can be represented many different ways. It doesn’t matter if you have 0x20 or 0x263. It’s still zero, right? Luckily, if you subtract these values from each other, they will always produce a difference of zero, which will still fall between 0 plus or minus a delta of 0. So it still works!
Double precision floating point numbers use a much smaller multiplier, again approximating a single bit of error.
If you don’t like these ranges and you want to make your floating point equality assertions less strict, you can change these multipliers to whatever you like by defining UNITY_FLOAT_PRECISION and UNITY_DOUBLE_PRECISION. See Unity documentation for more.
It’s “fun” that C is a standard where something as fundamental as an integer
varies by target. According to the C standard, an int is to be the target’s
natural register size, and it should be at least 16-bits and a multiple of a
byte. It also guarantees an order of sizes:
char <= short <= int <= long <= long longMost often, int is 32-bits. In many cases in the embedded world, int is
16-bits. There are rare microcontrollers out there that have 24-bit integers,
and this remains perfectly standard C.
To make things even more interesting, there are compilers and targets out there that have a hard choice to make. What if their natural register size is 10-bits or 12-bits? Clearly they can’t fulfill both the requirement to be at least 16-bits AND the requirement to match the natural register size. In these situations, they often choose the natural register size, leaving us with something like this:
char (8 bit) <= short (12 bit) <= int (12 bit) <= long (16 bit)Um… yikes. It’s obviously breaking a rule or two… but they had to break SOME rules, so they made a choice.
When the C99 standard rolled around, it introduced alternate standard-size types. It also introduced macros for pulling in MIN/MAX values for your integer types. It’s glorious! Unfortunately, many embedded compilers can’t be relied upon to use the C99 types (Sometimes because they have weird register sizes as described above. Sometimes because they don’t feel like it?).
A goal of Unity from the beginning was to support every combination of microcontroller or microprocessor and C compiler. Over time, we’ve gotten really close to this. There are a few tricks that you should be aware of, though, if you’re going to do this effectively on some of these more idiosyncratic targets.
First, when setting up Unity for a new target, you’re going to want to pay special attention to the macros for automatically detecting types (where available) or manually configuring them yourself. You can get information on both of these in Unity’s documentation.
What about the times where you suddenly need to deal with something odd, like a
24-bit int? The simplest solution is to use the next size up. If you have a
24-bit int, configure Unity to use 32-bit integers. If you have a 12-bit
int, configure Unity to use 16 bits. There are two ways this is going to
affect you:
- When Unity displays errors for you, it’s going to pad the upper unused bits with zeros.
- You’re going to have to be careful of assertions that perform signed
operations, particularly
TEST_ASSERT_INT_WITHIN. Such assertions might wrap yourintin the wrong place, and you could experience false failures. You can always back down to a simpleTEST_ASSERTand do the operations yourself.
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