Re: [RFC PATCH 1/2] Add C TAP harness

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Calvin

On 28/04/2023 17:31, Calvin Wan wrote:
> On Thu, Apr 27, 2023 at 1:15 PM Phillip Wood <phillip.wood123@gmail.com> wrote:
>>
>> Hi Calvin
>>
>> On 27/04/2023 18:50, Calvin Wan wrote:
>>> Introduces the C TAP harness from https://github.com/rra/c-tap-harness/
>>>
>>> There is also more complete documentation at
>>> https://www.eyrie.org/~eagle/software/c-tap-harness/
>>
>> I'm afraid this reply is rather briefer than I'd like but I'm short of
>> time and about to go off-list for a couple of weeks. My ideal unit test
>> library would
>>
>>    - print the file and line number of failed assertions
> 
> This library does print the file and line number of failed assertions.
> You can add a failing test in a new test file to check that this is
> the case.

I should have been clear that I was talking about is_int()
etc. provided by this library. They do not print the location of the
failing call as they are functions and therefore cannot know the
source location of the call unless they are wrapped in a macro which
passes the source location to them. The is_int() functions also print
an ok line for each check meaning that unless the test author comes up
with a unique description for each comparison it is hard to tell which
line a failing test comes from.

>>    - allow the test plan to be omitted by calling test_done() at the end
>>      of the test file as we do in our main test suite.
> 
> The same functionality can be achieved by adding some logic to adjust
> the number of planned tests and return early if necessary.

I'm afraid I don't understand your comment. My concern is that having
an explicit plan is a pain to maintain. Æver has pointed out elsewhere
in this thread that requiring an explicit plan is a good source of
merge conflicts.

>>    - support the TODO directive
> 
> This would be a nice feature to add to the library, however, I don't
> think it's necessary in a first pass.

It may not be necessary now, but if we think we want to add it in the
future we should look to see how easy that would be.

>>    - allow named tests (this maybe more trouble that it is worth as I
>>      think it inevitably leads to more boilerplate code calling the named
>>      tests)
> 
> I'm not quite sure what you're referring to with "named tests". Could
> you clarify (possibly with an example)?

I'd like to be able to have several checks within a test and get one
line of output if it passes. I'd also like the test framework to
manage the pass/fail state based on the checks in the test. For
example

	static void t_static_init(void)
	{
		struct strbuf buf = STRBUF_INIT;

		check_uint(buf.len, ==, 0);
		check_uint(buf.alloc, ==, 0);
		if (check(buf.buf == strbuf_slopbuf))
			return; /* avoid de-referencing buf.buf */
		check_char(buf.buf[0], ==, '\0');
	}

Would produce

	ok 1 - static initialization works

Using is_int() etc from this library would result in one line of output
for each check and require a description for each check which would
quickly become tedious.

The patch at the end of this email implements a test framework that
supports tests like the one above. The pass/fail state of tests is
managed by the framework based on the checks in each test
test. Failing checks produce informative messages to aid debugging,
for example

	# check "!strcmp(x, "hello")" failed at my-test.c:102
	#    left: "bye"
	#   right: "hello"

So one can quickly find the failing line in the test file and see what
the arguments to the test were.

>> Unfortunately this library doesn't seem to offer any of those features.
>> It does support a lazy test plan but uses atexit() so will not detect if
>> the test program exits before all the tests have run. I think it would
>> be useful to add some unit tests to our test suite and maybe this
>> library could form the basis of that but I think printing the file and
>> line number of failed assertions is pretty essential.
> 
> Since I've addressed your concerns regarding printing file and line
> numbers for failed assertions, do you think this test library is
> sufficient as a base to iterate off of? 

It would be possible, but I'd want to see some macros for checking
invariants that print the source location as well as their
arguments. I'd be interested to hear what you think of the alternative
approach in the patch below. The patch can be fetched with

git fetch https://github.com/phillipwood/git unit-tests

Best Wishes

Phillip

---- >8 ----
From: Phillip Wood <phillip.wood@dunelm.org.uk>

[RFC PATCH] unit-tests: proof of concept test framework

This patch contains a proof of concept implementation for writing unit
tests with TAP output. Each test is a function that contains one or more
checks. The test is run with the TEST() macro and if any of the checks
fail then the test will fail. A complete program that tests STRBUF_INIT
would look like

     #include "test-lib.h"
     #include "strbuf.h"

     static void t_static_init(void)
     {
             struct strbuf buf = STRBUF_INIT;

             check_uint(buf.len, ==, 0);
             check_uint(buf.alloc, ==, 0);
             if (check(buf.buf == strbuf_slopbuf))
		    return; /* avoid SIGSEV */
             check_char(buf.buf[0], ==, '\0');
     }

     int main(void)
     {
             TEST(t_static_init(), "static initialization works);

             return test_done();
     }

The output of this program would be

     ok 1 - static initialization works
     1..1

If any of the checks in a test fail then they print a diagnostic message
to aid debugging and the test will be reported as failing. For example a
failing integer check would look like

     # check "x >= 3" failed at my-test.c:102
     #    left: 2
     #   right: 3
     not ok 1 - x is greater than or equal to three

There are a number of check functions implemented so far. check() checks
a boolean condition, check_int(), check_uint() and check_char() take two
values to compare and a comparison operator. check_str() will check if
two strings are equal. Custom checks are simple to implement as shown in
the comments above test_assert() in test-lib.h.

Tests can be skipped with test_skip() which can be supplied with a
reason for skipping which it will print. Tests can print diagnostic
messages with test_msg().  Checks that are known to fail can be wrapped
in TEST_TODO().

There are a couple of example test programs included in this
patch. t-basic.c implements some self-tests and demonstrates the
diagnostic output for failing test. The output of this program is
checked by t0080-unit-test-output.sh. t-strbuf.c shows some example
unit tests for strbuf.c

The unit tests can be built with "make unit-tests" (this works but the
Makefile changes need some further work). Once they have been built they
can be run manually (e.g t/unit-tests/t-strbuf) or with prove.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
  Makefile                    |  23 ++-
  t/t0080-unit-test-output.sh |  58 +++++++
  t/unit-tests/.gitignore     |   2 +
  t/unit-tests/t-basic.c      |  87 ++++++++++
  t/unit-tests/t-strbuf.c     |  75 ++++++++
  t/unit-tests/test-lib.c     | 329 ++++++++++++++++++++++++++++++++++++
  t/unit-tests/test-lib.h     | 143 ++++++++++++++++
  7 files changed, 715 insertions(+), 2 deletions(-)
  create mode 100755 t/t0080-unit-test-output.sh
  create mode 100644 t/unit-tests/.gitignore
  create mode 100644 t/unit-tests/t-basic.c
  create mode 100644 t/unit-tests/t-strbuf.c
  create mode 100644 t/unit-tests/test-lib.c
  create mode 100644 t/unit-tests/test-lib.h

diff --git a/Makefile b/Makefile
index e440728c24..f0ca5bae4b 100644
--- a/Makefile
+++ b/Makefile
@@ -681,6 +681,7 @@ SCRIPT_LIB =
  TEST_BUILTINS_OBJS =
  TEST_OBJS =
  TEST_PROGRAMS_NEED_X =
+UNIT_TEST_PROGRAMS =
  THIRD_PARTY_SOURCES =
  
  # Having this variable in your environment would break pipelines because
@@ -2665,13 +2666,20 @@ SCALAR_OBJS += scalar.o
  .PHONY: scalar-objs
  scalar-objs: $(SCALAR_OBJS)
  
+UNIT_TEST_PROGRAMS += t-basic
+UNIT_TEST_PROGRAMS += t-strbuf
+UNIT_TEST_PROGS = $(patsubst %,t/unit-tests/%$X,$(UNIT_TEST_PROGRAMS))
+UNIT_TEST_OBJS = $(patsubst %,t/unit-tests/%.o,$(UNIT_TEST_PROGRAMS))
+UNIT_TEST_OBJS += t/unit-tests/test-lib.o
+
  OBJECTS += $(GIT_OBJS)
  OBJECTS += $(SCALAR_OBJS)
  OBJECTS += $(PROGRAM_OBJS)
  OBJECTS += $(TEST_OBJS)
  OBJECTS += $(XDIFF_OBJS)
  OBJECTS += $(FUZZ_OBJS)
  OBJECTS += $(REFTABLE_OBJS) $(REFTABLE_TEST_OBJS)
+OBJECTS += $(UNIT_TEST_OBJS)
  
  ifndef NO_CURL
  	OBJECTS += http.o http-walker.o remote-curl.o
@@ -3167,7 +3175,7 @@ endif
  
  test_bindir_programs := $(patsubst %,bin-wrappers/%,$(BINDIR_PROGRAMS_NEED_X) $(BINDIR_PROGRAMS_NO_X) $(TEST_PROGRAMS_NEED_X))
  
-all:: $(TEST_PROGRAMS) $(test_bindir_programs)
+all:: $(TEST_PROGRAMS) $(test_bindir_programs) $(UNIT_TEST_PROGS)
  
  bin-wrappers/%: wrap-for-bin.sh
  	$(call mkdir_p_parent_template)
@@ -3592,7 +3600,7 @@ endif
  
  artifacts-tar:: $(ALL_COMMANDS_TO_INSTALL) $(SCRIPT_LIB) $(OTHER_PROGRAMS) \
  		GIT-BUILD-OPTIONS $(TEST_PROGRAMS) $(test_bindir_programs) \
-		$(MOFILES)
+		$(UNIT_TEST_PROGS) $(MOFILES)
  	$(QUIET_SUBDIR0)templates $(QUIET_SUBDIR1) \
  		SHELL_PATH='$(SHELL_PATH_SQ)' PERL_PATH='$(PERL_PATH_SQ)'
  	test -n "$(ARTIFACTS_DIRECTORY)"
@@ -3831,3 +3839,14 @@ $(FUZZ_PROGRAMS): all
  		$(XDIFF_OBJS) $(EXTLIBS) git.o $@.o $(LIB_FUZZING_ENGINE) -o $@
  
  fuzz-all: $(FUZZ_PROGRAMS)
+
+t/unit-tests/t-basic$X: t/unit-tests/t-basic.o t/unit-tests/test-lib.o $(GITLIBS) GIT-LDFLAGS
+	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) \
+		 $(filter %.o,$^) $(filter %.a,$^) $(LIBS)
+
+t/unit-tests/t-strbuf$X: t/unit-tests/t-strbuf.o t/unit-tests/test-lib.o $(GITLIBS) GIT-LDFLAGS
+	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) \
+		 $(filter %.o,$^) $(filter %.a,$^) $(LIBS)
+
+.PHONY: unit-tests
+unit-tests: $(UNIT_TEST_PROGS)
diff --git a/t/t0080-unit-test-output.sh b/t/t0080-unit-test-output.sh
new file mode 100755
index 0000000000..c60e402260
--- /dev/null
+++ b/t/t0080-unit-test-output.sh
@@ -0,0 +1,58 @@
+#!/bin/sh
+
+test_description='Test the output of the unit test framework'
+
+. ./test-lib.sh
+
+test_expect_success 'TAP output from unit tests' '
+	cat >expect <<-EOF &&
+	ok 1 - passing test
+	ok 2 - passing test and assertion return 0
+	# check "1 == 2" failed at t/unit-tests/t-basic.c:68
+	#    left: 1
+	#   right: 2
+	not ok 3 - failing test
+	ok 4 - failing test and assertion return -1
+	not ok 5 - passing TEST_TODO() # TODO
+	ok 6 - passing TEST_TODO() returns 0
+	# todo check ${SQ}check(x)${SQ} succeeded at t/unit-tests/t-basic.c:17
+	not ok 7 - failing TEST_TODO()
+	ok 8 - failing TEST_TODO() returns -1
+	# check "0" failed at t/unit-tests/t-basic.c:22
+	# skipping test - missing prerequisite
+	# skipping check ${SQ}1${SQ} at t/unit-tests/t-basic.c:24
+	ok 9 - test_skip() # SKIP
+	ok 10 - skipped test returns 0
+	# skipping test - missing prerequisite
+	ok 11 - test_skip() inside TEST_TODO() # SKIP
+	ok 12 - test_skip() inside TEST_TODO() returns 0
+	# check "0" failed at t/unit-tests/t-basic.c:40
+	not ok 13 - TEST_TODO() after failing check
+	ok 14 - TEST_TODO() after failing check returns -1
+	# check "0" failed at t/unit-tests/t-basic.c:48
+	not ok 15 - failing check after TEST_TODO()
+	ok 16 - failing check after TEST_TODO() returns -1
+	# check "!strcmp("\thello\\\\", "there\"\n")" failed at t/unit-tests/t-basic.c:53
+	#    left: "\011hello\\\\"
+	#   right: "there\"\012"
+	# check "!strcmp("NULL", NULL)" failed at t/unit-tests/t-basic.c:54
+	#    left: "NULL"
+	#   right: NULL
+	# check "${SQ}a${SQ} == ${SQ}\n${SQ}" failed at t/unit-tests/t-basic.c:55
+	#    left: ${SQ}a${SQ}
+	#   right: ${SQ}\012${SQ}
+	# check "${SQ}\\\\${SQ} == ${SQ}\\${SQ}${SQ}" failed at t/unit-tests/t-basic.c:56
+	#    left: ${SQ}\\\\${SQ}
+	#   right: ${SQ}\\${SQ}${SQ}
+	not ok 17 - messages from failing string and char comparison
+	# BUG: test has no checks at t/unit-tests/t-basic.c:83
+	not ok 18 - test with no checks
+	ok 19 - test with no checks returns -1
+	1..19
+	EOF
+
+	! "$GIT_BUILD_DIR"/t/unit-tests/t-basic >actual &&
+	test_cmp expect actual
+'
+
+test_done
diff --git a/t/unit-tests/.gitignore b/t/unit-tests/.gitignore
new file mode 100644
index 0000000000..e292d58348
--- /dev/null
+++ b/t/unit-tests/.gitignore
@@ -0,0 +1,2 @@
+/t-basic
+/t-strbuf
diff --git a/t/unit-tests/t-basic.c b/t/unit-tests/t-basic.c
new file mode 100644
index 0000000000..ab0b7682c4
--- /dev/null
+++ b/t/unit-tests/t-basic.c
@@ -0,0 +1,87 @@
+#include "test-lib.h"
+
+/* Used to store the return value of check_int(). */
+static int check_res;
+
+/* Used to store the return value of TEST(). */
+static int test_res;
+
+static void t_res(int expect)
+{
+	check_int(check_res, ==, expect);
+	check_int(test_res, ==, expect);
+}
+
+static void t_todo(int x)
+{
+	check_res = TEST_TODO(check(x));
+}
+
+static void t_skip(void)
+{
+	check(0);
+	test_skip("missing prerequisite");
+	check(1);
+}
+
+static int do_skip(void)
+{
+	test_skip("missing prerequisite");
+	return 0;
+}
+
+static void t_skip_todo(void)
+{
+	check_res = TEST_TODO(do_skip());
+}
+
+static void t_todo_after_fail(void)
+{
+	check(0);
+	TEST_TODO(check(0));
+}
+
+static void t_fail_after_todo(void)
+{
+	check(1);
+	TEST_TODO(check(0));
+	check(0);
+}
+
+static void t_messages(void)
+{
+	check_str("\thello\\", "there\"\n");
+	check_str("NULL", NULL);
+	check_char('a', ==, '\n');
+	check_char('\\', ==, '\'');
+}
+
+static void t_empty(void)
+{
+	; /* empty */
+}
+
+int cmd_main(int argc, const char **argv)
+{
+	test_res = TEST(check_res = check_int(1, ==, 1), "passing test");
+	TEST(t_res(0), "passing test and assertion return 0");
+	test_res = TEST(check_res = check_int(1, ==, 2), "failing test");
+	TEST(t_res(-1), "failing test and assertion return -1");
+	test_res = TEST(t_todo(0), "passing TEST_TODO()");
+	TEST(t_res(0), "passing TEST_TODO() returns 0");
+	test_res = TEST(t_todo(1), "failing TEST_TODO()");
+	TEST(t_res(-1), "failing TEST_TODO() returns -1");
+	test_res = TEST(t_skip(), "test_skip()");
+	TEST(check_int(test_res, ==, 0), "skipped test returns 0");
+	test_res = TEST(t_skip_todo(), "test_skip() inside TEST_TODO()");
+	TEST(t_res(0), "test_skip() inside TEST_TODO() returns 0");
+	test_res = TEST(t_todo_after_fail(), "TEST_TODO() after failing check");
+	TEST(check_int(test_res, ==, -1), "TEST_TODO() after failing check returns -1");
+	test_res = TEST(t_fail_after_todo(), "failing check after TEST_TODO()");
+	TEST(check_int(test_res, ==, -1), "failing check after TEST_TODO() returns -1");
+	TEST(t_messages(), "messages from failing string and char comparison");
+	test_res = TEST(t_empty(), "test with no checks");
+	TEST(check_int(test_res, ==, -1), "test with no checks returns -1");
+
+	return test_done();
+}
diff --git a/t/unit-tests/t-strbuf.c b/t/unit-tests/t-strbuf.c
new file mode 100644
index 0000000000..561611e242
--- /dev/null
+++ b/t/unit-tests/t-strbuf.c
@@ -0,0 +1,75 @@
+#include "test-lib.h"
+#include "strbuf.h"
+
+/* wrapper that supplies tests with an initialized strbuf */
+static void setup(void (*f)(struct strbuf*, void*), void *data)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	f(&buf, data);
+	strbuf_release(&buf);
+	check_uint(buf.len, ==, 0);
+	check_uint(buf.alloc, ==, 0);
+	check(buf.buf == strbuf_slopbuf);
+	check_char(buf.buf[0], ==, '\0');
+}
+
+static void t_static_init(void)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	check_uint(buf.len, ==, 0);
+	check_uint(buf.alloc, ==, 0);
+	if (check(buf.buf == strbuf_slopbuf))
+		return; /* avoid de-referencing buf.buf */
+	check_char(buf.buf[0], ==, '\0');
+}
+
+static void t_dynamic_init(void)
+{
+	struct strbuf buf;
+
+	strbuf_init(&buf, 1024);
+	check_uint(buf.len, ==, 0);
+	check_uint(buf.alloc, >=, 1024);
+	check_char(buf.buf[0], ==, '\0');
+	strbuf_release(&buf);
+}
+
+static void t_addch(struct strbuf *buf, void *data)
+{
+	const char *p_ch = data;
+	const char ch = *p_ch;
+
+	strbuf_addch(buf, ch);
+	if (check_uint(buf->len, ==, 1) ||
+	    check_uint(buf->alloc, >, 1))
+		return; /* avoid de-referencing buf->buf */
+	check_char(buf->buf[0], ==, ch);
+	check_char(buf->buf[1], ==, '\0');
+}
+
+static void t_addstr(struct strbuf *buf, void *data)
+{
+	const char *text = data;
+	size_t len = strlen(text);
+
+	strbuf_addstr(buf, text);
+	if (check_uint(buf->len, ==, len) ||
+	    check_uint(buf->alloc, >, len) ||
+	    check_char(buf->buf[len], ==, '\0'))
+	    return;
+	check_str(buf->buf, text);
+}
+
+int cmd_main(int argc, const char **argv)
+{
+	if (TEST(t_static_init(), "static initialization works"))
+		test_skip_all("STRBUF_INIT is broken");
+	TEST(t_dynamic_init(), "dynamic initialization works");
+	TEST(setup(t_addch, "a"), "strbuf_addch adds char");
+	TEST(setup(t_addch, ""), "strbuf_addch adds NUL char");
+	TEST(setup(t_addstr, "hello there"), "strbuf_addstr adds string");
+
+	return test_done();
+}
diff --git a/t/unit-tests/test-lib.c b/t/unit-tests/test-lib.c
new file mode 100644
index 0000000000..70030d587f
--- /dev/null
+++ b/t/unit-tests/test-lib.c
@@ -0,0 +1,329 @@
+#include "test-lib.h"
+
+enum result {
+	RESULT_NONE,
+	RESULT_FAILURE,
+	RESULT_SKIP,
+	RESULT_SUCCESS,
+	RESULT_TODO
+};
+
+static struct {
+	enum result result;
+	int count;
+	unsigned failed :1;
+	unsigned lazy_plan :1;
+	unsigned running :1;
+	unsigned skip_all :1;
+	unsigned todo :1;
+} ctx = {
+	.lazy_plan = 1,
+	.result = RESULT_NONE,
+};
+
+static void msg_with_prefix(const char *prefix, const char *format, va_list ap)
+{
+	fflush(stderr);
+	if (prefix)
+		fprintf(stdout, "%s", prefix);
+	vprintf(format, ap); /* TODO: handle newlines */
+	putc('\n', stdout);
+	fflush(stdout);
+}
+
+void test_msg(const char *format, ...)
+{
+	va_list ap;
+
+	va_start(ap, format);
+	msg_with_prefix("# ", format, ap);
+	va_end(ap);
+}
+
+void test_plan(int count)
+{
+	assert(!ctx.running);
+
+	fflush(stderr);
+	printf("1..%d\n", count);
+	fflush(stdout);
+	ctx.lazy_plan = 0;
+}
+
+int test_done(void)
+{
+	assert(!ctx.running);
+
+	if (ctx.lazy_plan)
+		test_plan(ctx.count);
+
+	return ctx.failed;
+}
+
+void test_skip(const char *format, ...)
+{
+	va_list ap;
+
+	assert(ctx.running);
+
+	ctx.result = RESULT_SKIP;
+	va_start(ap, format);
+	if (format)
+		msg_with_prefix("# skipping test - ", format, ap);
+	va_end(ap);
+}
+
+void test_skip_all(const char *format, ...)
+{
+	va_list ap;
+	const char *prefix;
+
+	if (!ctx.count && ctx.lazy_plan) {
+		/* We have not printed a test plan yet */
+		prefix = "1..0 # SKIP ";
+		ctx.lazy_plan = 0;
+	} else {
+		/* We have already printed a test plan */
+		prefix = "Bail out! # ";
+		ctx.failed = 1;
+	}
+	ctx.skip_all = 1;
+	ctx.result = RESULT_SKIP;
+	va_start(ap, format);
+	msg_with_prefix(prefix, format, ap);
+	va_end(ap);
+}
+
+int test__run_begin(void)
+{
+	assert(!ctx.running);
+
+	ctx.count++;
+	ctx.result = RESULT_NONE;
+	ctx.running = 1;
+
+	return ctx.skip_all;
+}
+
+static void print_description(const char *format, va_list ap)
+{
+	if (format) {
+		fputs(" - ", stdout);
+		vprintf(format, ap);
+	}
+}
+
+int test__run_end(int was_run UNUSED, const char *location, const char *format, ...)
+{
+	va_list ap;
+
+	assert(ctx.running);
+	assert(!ctx.todo);
+
+	fflush(stderr);
+	va_start(ap, format);
+	if (!ctx.skip_all) {
+		switch (ctx.result) {
+		case RESULT_SUCCESS:
+			printf("ok %d", ctx.count);
+			print_description(format, ap);
+			break;
+
+		case RESULT_FAILURE:
+			printf("not ok %d", ctx.count);
+			print_description(format, ap);
+			break;
+
+		case RESULT_TODO:
+			printf("not ok %d", ctx.count);
+			print_description(format, ap);
+			printf(" # TODO");
+			break;
+
+		case RESULT_SKIP:
+			printf("ok %d", ctx.count);
+			print_description(format, ap);
+			printf(" # SKIP");
+			break;
+
+		case RESULT_NONE:
+			test_msg("BUG: test has no checks at %s", location);
+			printf("not ok %d", ctx.count);
+			print_description(format, ap);
+			ctx.result = RESULT_FAILURE;
+			break;
+		}
+	}
+	va_end(ap);
+	ctx.running = 0;
+	if (ctx.skip_all)
+		return 0;
+	putc('\n', stdout);
+	fflush(stdout);
+	ctx.failed |= ctx.result == RESULT_FAILURE;
+
+	return -(ctx.result == RESULT_FAILURE);
+}
+
+static void test_fail(void)
+{
+	assert(ctx.result != RESULT_SKIP);
+
+	ctx.result = RESULT_FAILURE;
+}
+
+static void test_pass(void)
+{
+	assert(ctx.result != RESULT_SKIP);
+
+	if (ctx.result == RESULT_NONE)
+		ctx.result = RESULT_SUCCESS;
+}
+
+static void test_todo(void)
+{
+	assert(ctx.result != RESULT_SKIP);
+
+	if (ctx.result != RESULT_FAILURE)
+		ctx.result = RESULT_TODO;
+}
+
+int test_assert(const char *location, const char *check, int ok)
+{
+	assert(ctx.running);
+
+	if (ctx.result == RESULT_SKIP) {
+		test_msg("skipping check '%s' at %s", check, location);
+		return 0;
+	} else if (!ctx.todo) {
+		if (ok) {
+			test_pass();
+		} else {
+			test_msg("check \"%s\" failed at %s", check, location);
+			test_fail();
+		}
+	}
+
+	return -!ok;
+}
+
+void test__todo_begin(void)
+{
+	assert(ctx.running);
+	assert(!ctx.todo);
+
+	ctx.todo = 1;
+}
+
+int test__todo_end(const char *location, const char *check, int res)
+{
+	assert(ctx.running);
+	assert(ctx.todo);
+
+	ctx.todo = 0;
+	if (ctx.result == RESULT_SKIP)
+		return 0;
+	if (!res) {
+		test_msg("todo check '%s' succeeded at %s", check, location);
+		test_fail();
+	} else {
+		test_todo();
+	}
+
+	return -!res;
+}
+
+int check_bool_loc(const char *loc, const char *check, int ok)
+{
+	return test_assert(loc, check, ok);
+}
+
+union test__tmp test__tmp[2];
+
+int check_int_loc(const char *loc, const char *check, int ok,
+		  intmax_t a, intmax_t b)
+{
+	int ret = test_assert(loc, check, ok);
+
+	if (ret) {
+		test_msg("   left: %"PRIdMAX, a);
+		test_msg("  right: %"PRIdMAX, b);
+	}
+
+	return ret;
+}
+
+int check_uint_loc(const char *loc, const char *check, int ok,
+		   uintmax_t a, uintmax_t b)
+{
+	int ret = test_assert(loc, check, ok);
+
+	if (ret) {
+		test_msg("   left: %"PRIuMAX, a);
+		test_msg("  right: %"PRIuMAX, b);
+	}
+
+	return ret;
+}
+
+static void print_one_char(char ch, char quote)
+{
+	if ((unsigned char)ch < 0x20u || ch == 0x7f) {
+		/* TODO: improve handling of \a, \b, \f ... */
+		printf("\\%03o", (unsigned char)ch);
+	} else {
+		if (ch == '\\' || ch == quote)
+			putc('\\', stdout);
+		putc(ch, stdout);
+	}
+}
+
+static void print_char(const char *prefix, char ch)
+{
+	printf("# %s: '", prefix);
+	print_one_char(ch, '\'');
+	fputs("'\n", stdout);
+}
+
+int check_char_loc(const char *loc, const char *check, int ok, char a, char b)
+{
+	int ret = test_assert(loc, check, ok);
+
+	if (ret) {
+		fflush(stderr);
+		print_char("   left", a);
+		print_char("  right", b);
+		fflush(stdout);
+	}
+
+	return ret;
+}
+
+static void print_str(const char *prefix, const char *str)
+{
+	printf("# %s: ", prefix);
+	if (!str) {
+		fputs("NULL\n", stdout);
+	} else {
+		putc('"', stdout);
+		while (*str)
+			print_one_char(*str++, '"');
+		fputs("\"\n", stdout);
+	}
+}
+
+int check_str_loc(const char *loc, const char *check,
+		  const char *a, const char *b)
+{
+	int ok = (!a && !b) || (a && b && !strcmp(a, b));
+	int ret = test_assert(loc, check, ok);
+
+	if (ret) {
+		fflush(stderr);
+		print_str("   left", a);
+		print_str("  right", b);
+		fflush(stdout);
+	}
+
+	return ret;
+}
diff --git a/t/unit-tests/test-lib.h b/t/unit-tests/test-lib.h
new file mode 100644
index 0000000000..720c97c6f8
--- /dev/null
+++ b/t/unit-tests/test-lib.h
@@ -0,0 +1,143 @@
+#ifndef TEST_LIB_H
+#define TEST_LIB_H
+
+#include "git-compat-util.h"
+
+/*
+ * Run a test function, returns 0 if the test succeeds, -1 if it
+ * fails. If test_skip_all() has been called then the test will not be
+ * run. The description for each test should be unique. For example:
+ *
+ *  TEST(test_something(arg1, arg2), "something %d %d", arg1, arg2)
+ */
+#define TEST(t, ...)					\
+	test__run_end(test__run_begin() ? 0 : (t, 1),	\
+		      TEST_LOCATION(),  __VA_ARGS__)
+
+/*
+ * Print a test plan, should be called before any tests. If the number
+ * of tests is not known in advance test_done() will automatically
+ * print a plan at the end of the test program.
+ */
+void test_plan(int count);
+
+/*
+ * test_done() must be called at the end of main(). It will print the
+ * plan if plan() was not called at the beginning of the test program
+ * and returns the exit code for the test program.
+ */
+int test_done(void);
+
+/* Skip the current test. */
+__attribute__((format (printf, 1, 2)))
+void test_skip(const char *format, ...);
+
+/* Skip all remaining tests. */
+__attribute__((format (printf, 1, 2)))
+void test_skip_all(const char *format, ...);
+
+/* Print a diagnostic message to stdout. */
+__attribute__((format (printf, 1, 2)))
+void test_msg(const char *format, ...);
+
+/*
+ * Test checks are built around test_assert(). checks return 0 on
+ * success, -1 on failure. If any check fails then the test will
+ * fail. To create a custom check define a function that wraps
+ * test_assert() and a macro to wrap that function. For example:
+ *
+ *  static int check_oid_loc(const char *loc, const char *check,
+ *			     struct object_id *a, struct object_id *b)
+ *  {
+ *	    int res = test_assert(loc, check, oideq(a, b));
+ *
+ *	    if (res) {
+ *		    test_msg("   left: %s", oid_to_hex(a);
+ *		    test_msg("  right: %s", oid_to_hex(a);
+ *
+ *	    }
+ *	    return res;
+ *  }
+ *
+ *  #define check_oid(a, b) \
+ *	    check_oid_loc(TEST_LOCATION(), "oideq("#a", "#b")", a, b)
+ */
+int test_assert(const char *location, const char *check, int ok);
+
+/* Helper macro to pass the location to checks */
+#define TEST_LOCATION() TEST__MAKE_LOCATION(__LINE__)
+
+/* Check a boolean condition. */
+#define check(x)				\
+	check_bool_loc(TEST_LOCATION(), #x, x)
+int check_bool_loc(const char *loc, const char *check, int ok);
+
+/*
+ * Compare two integers. Prints a message with the two values if the
+ * comparison fails. NB this is not thread safe.
+ */
+#define check_int(a, op, b)						\
+	(test__tmp[0].i = (a), test__tmp[1].i = (b),			\
+	 check_int_loc(TEST_LOCATION(), #a" "#op" "#b,			\
+		       test__tmp[0].i op test__tmp[1].i, a, b))
+int check_int_loc(const char *loc, const char *check, int ok,
+		  intmax_t a, intmax_t b);
+
+/*
+ * Compare two unsigned integers. Prints a message with the two values
+ * if the comparison fails. NB this is not thread safe.
+ */
+#define check_uint(a, op, b)						\
+	(test__tmp[0].u = (a), test__tmp[1].u = (b),			\
+	 check_uint_loc(TEST_LOCATION(), #a" "#op" "#b,			\
+			test__tmp[0].u op test__tmp[1].u, a, b))
+int check_uint_loc(const char *loc, const char *check, int ok,
+		   uintmax_t a, uintmax_t b);
+
+/*
+ * Compare two chars. Prints a message with the two values if the
+ * comparison fails. NB this is not thread safe.
+ */
+#define check_char(a, op, b)						\
+	(test__tmp[0].c = (a), test__tmp[1].c = (b),			\
+	 check_char_loc(TEST_LOCATION(), #a" "#op" "#b,			\
+			test__tmp[0].c op test__tmp[1].c, a, b))
+int check_char_loc(const char *loc, const char *check, int ok,
+		   char a, char b);
+
+/* Check whether two strings are equal. */
+#define check_str(a, b)							\
+	check_str_loc(TEST_LOCATION(), "!strcmp("#a", "#b")", a, b)
+int check_str_loc(const char *loc, const char *check,
+		  const char *a, const char *b);
+
+/*
+ * Wrap a check that is known to fail. If the check succeeds then the
+ * test will fail. Returns 0 if the check fails, -1 if it
+ * succeeds. For example:
+ *
+ *  TEST_TODO(check(0));
+ */
+#define TEST_TODO(check) \
+	(test__todo_begin(), test__todo_end(TEST_LOCATION(), #check, check))
+
+/* Private helpers */
+
+#define TEST__STR(x) #x
+#define TEST__MAKE_LOCATION(line) __FILE__ ":" TEST__STR(line)
+
+union test__tmp {
+	intmax_t i;
+	uintmax_t u;
+	char c;
+};
+
+extern union test__tmp test__tmp[2];
+
+int test__run_begin(void);
+__attribute__((format (printf, 3, 4)))
+int test__run_end(int, const char *, const char *, ...);
+void test__todo_begin(void);
+int test__todo_end(const char *, const char *, int);
+
+#endif /* TEST_LIB_H */
-- 
2.40.0.685.gf2f8f6435f