diff --git a/cddl/lib/libtpool/Makefile b/cddl/lib/libtpool/Makefile
--- a/cddl/lib/libtpool/Makefile
+++ b/cddl/lib/libtpool/Makefile
@@ -23,4 +23,9 @@
 CFLAGS+= -DHAVE_ISSETUGID 
 CFLAGS+= -include ${SRCTOP}/sys/modules/zfs/zfs_config.h
 
+.include <src.opts.mk>
+
+HAS_TESTS=
+SUBDIR.${MK_TESTS}+=	tests
+
 .include <bsd.lib.mk>
diff --git a/cddl/lib/libtpool/tests/Makefile b/cddl/lib/libtpool/tests/Makefile
new file mode 100644
--- /dev/null
+++ b/cddl/lib/libtpool/tests/Makefile
@@ -0,0 +1,12 @@
+ZFSTOP= ${SRCTOP}/sys/contrib/openzfs
+
+ATF_TESTS_C+=	libtpool_test
+
+TEST_METADATA+= timeout="10"
+
+CFLAGS+=	-I${ZFSTOP}/include \
+		-I${ZFSTOP}/lib/libspl/include
+
+LIBADD+=	pthread tpool
+
+.include <bsd.test.mk>
diff --git a/cddl/lib/libtpool/tests/libtpool_test.c b/cddl/lib/libtpool/tests/libtpool_test.c
new file mode 100644
--- /dev/null
+++ b/cddl/lib/libtpool/tests/libtpool_test.c
@@ -0,0 +1,78 @@
+#include <sys/stdtypes.h>
+#include <sys/sysctl.h>
+#include <errno.h>
+#include <pthread.h>
+
+#include <thread_pool.h>
+
+#include <atf-c.h>
+
+static void
+tp_delay(void *arg)
+{
+	pthread_barrier_t *barrier = arg;
+
+	/* Block this task until all thread pool workers have been created. */
+	pthread_barrier_wait(barrier);
+}
+
+/*
+ * NB: we could reduce the test's resource cost by using rctl(4).  But that
+ * isn't enabled by default.  And even with a thread limit of 1500, it takes <
+ * 0.1s to run on my machine.  So I don't think it's worth optimizing for the
+ * case where rctl is available.
+ */
+ATF_TC(complete_exhaustion);
+ATF_TC_HEAD(complete_exhaustion, tc)
+{
+	atf_tc_set_md_var(tc, "descr",
+	    "A thread pool should fail to schedule tasks if it is completely impossible to spawn any threads.");
+}
+
+ATF_TC_BODY(complete_exhaustion, tc)
+{
+	pthread_barrier_t barrier;
+	tpool_t *tp0, *tp1;
+	size_t len;
+	int max_threads_per_proc = 0;
+	int nworkers;
+	int r, i;
+
+
+	len = sizeof(max_threads_per_proc);
+	r = sysctlbyname("kern.threads.max_threads_per_proc",
+	    &max_threads_per_proc, &len, NULL, 0);
+	ATF_REQUIRE_EQ_MSG(r, 0, "sysctlbyname: %s", strerror(errno));
+	nworkers = max_threads_per_proc - 1;
+	pthread_barrier_init(&barrier, NULL, max_threads_per_proc);
+
+	/*
+	 * Create the first thread pool and spawn the maximum allowed number of
+	 * processes.
+	 */
+	tp0 = tpool_create(nworkers, nworkers, 1, NULL);
+	ATF_REQUIRE(tp0 != NULL);
+	for (i = 0; i < nworkers; i++) {
+		ATF_REQUIRE_EQ(tpool_dispatch(tp0, tp_delay, &barrier), 0);
+	}
+
+	/*
+	 * Now create a second thread pool.  Unable to create new threads, the
+	 * dispatch function should return an error.
+	 */
+	tp1 = tpool_create(nworkers, 2 * nworkers, 1, NULL);
+	ATF_REQUIRE(tp1 != NULL);
+	ATF_REQUIRE_EQ(tpool_dispatch(tp1, tp_delay, NULL), -1);
+
+	/* Cleanup */
+	ATF_REQUIRE_EQ(pthread_barrier_wait(&barrier), 0);
+	tpool_wait(tp1);
+	tpool_wait(tp0);
+}
+
+ATF_TP_ADD_TCS(tp)
+{
+	ATF_TP_ADD_TC(tp, complete_exhaustion);
+
+	return (atf_no_error());
+}
diff --git a/etc/mtree/BSD.tests.dist b/etc/mtree/BSD.tests.dist
--- a/etc/mtree/BSD.tests.dist
+++ b/etc/mtree/BSD.tests.dist
@@ -80,6 +80,8 @@
     ..
     cddl
         lib
+            libtpool
+            ..
         ..
         sbin
         ..