memblockq-test: Utility function to validate queue invariants

In particular, the relations between base, minreq, tlength, length,
missing, maxlength follow certain rules. On change, these invariants can
be violated, which requires additional code to restore them. Setting one
value can thus cause a cascade of changes. This utility function can
assert those invariants after changing something.

src/tests/memblockq-test.c

@@ -110,6 +110,68 @@ static void dump(pa_memblockq *bq, int n) {
     fprintf(stderr, "<\n");
 }
 
+/*
+ * utility function to validate invariants
+ *
+ * The different values like base, maxlength etc follow certain rules.
+ * This convenience function makes sure that changes don't violate
+ * these rules.
+ */
+static void check_queue_invariants(pa_memblockq *bq) {
+    size_t base = pa_memblockq_get_base(bq);
+    size_t maxlength = pa_memblockq_get_maxlength(bq);
+    size_t tlength = pa_memblockq_get_tlength(bq);
+    size_t minreq = pa_memblockq_get_minreq(bq);
+    size_t prebuf = pa_memblockq_get_prebuf(bq);
+    size_t length = pa_memblockq_get_length(bq);
+    size_t missing = pa_memblockq_missing(bq);
+
+    /* base > zero */
+    ck_assert_int_gt(base, 0);
+
+    /* maxlength multiple of base
+     * maxlength >= base */
+    ck_assert_int_eq(maxlength % base, 0);
+    ck_assert_int_ge(maxlength, base);
+
+    /* tlength multiple of base
+     * tlength >= base
+     * tlength <= maxlength */
+    ck_assert_int_eq(tlength % base, 0);
+    ck_assert_int_ge(tlength, base);
+    ck_assert_int_le(tlength, maxlength);
+
+    /* minreq multiple of base
+     * minreq >= base
+     * minreq <= tlength */
+    ck_assert_int_eq(minreq % base, 0);
+    ck_assert_int_ge(minreq, base);
+    ck_assert_int_le(minreq, tlength);
+
+    /* prebuf multiple of base
+     * prebuf >= 0
+     * prebuf <= tlength + base - minreq
+     * prebuf <= tlength (because minreq >= base) */
+    ck_assert_int_eq(prebuf % base, 0);
+    ck_assert_int_ge(prebuf, 0);
+    ck_assert_int_le(prebuf, tlength + base - minreq);
+    ck_assert_int_le(prebuf, tlength);
+
+    /* length >= 0
+     * length <= maxlength */
+    ck_assert_int_ge(length, 0);
+    ck_assert_int_le(length, maxlength);
+
+    /* missing >= 0
+     * missing <= tlength
+     * minimum reported amount of missing data is minreq
+     * reported amount of missing data is target length minus actual length */
+    ck_assert_int_ge(missing, 0);
+    ck_assert_int_le(missing, tlength);
+    ck_assert((missing == 0) || (missing >= minreq));
+    ck_assert((missing == 0) || (missing == tlength - length));
+}
+
 START_TEST (memchunk_from_str_test) {
     pa_mempool *p;
     pa_memchunk chunk;