X ΔBtail: Tweak tests to run faster in normal mode

t(TestΔBTailRandom) ~320s -> ~100s.

wcfs/internal/xbtree/xbtreetest/testing.go

@@ -32,6 +32,15 @@ var (
 	randseedFlag = flag.Int64("randseed", -1, `seed for random number generator`)
 )
 
+// VeryLong returns whether -verylong flag is in effect.
+func VeryLong() bool {
+	// -short takes priority over -verylong
+	if testing.Short() {
+		return false
+	}
+	return *verylongFlag
+}
+
 // N returns short, medium, or long depending on whether tests were ran with
 // -short, -verylong, or  normally.
 func N(short, medium, long int) int {

wcfs/internal/xbtree/δbtail_test.go

@@ -476,7 +476,7 @@ func TestΔBTailRandom(t *testing.T) {
 	// in non-short mode rebuild tests are exercising more keys variants, plus every test case
 	// takes more time. Compensate for that as well.
 	if !testing.Short() {
-		nrebuild -= 3
+		nrebuild -= 4
 	}
 
 	testq := make(chan ΔBTestEntry)
@@ -909,11 +909,11 @@ func xverifyΔBTail_rebuild(t *testing.T, db *zodb.DB, treeRoot zodb.Oid, t0, t1
 						/*vδT=*/ δkv1_k1R2, δkv2_k1R2)
 
 					// tRestKeys2      = tAllKeys - keys1
-					// reduce that to  = tAllKeys - keys1R2   in short mode
+					// reduce that to  = tAllKeys - keys1R2   in short/medium mode
 					// ( if key from keys2 already became tracked after Track(keys1) + Update,
 					//   adding Track(that-key), is not adding much testing coverage to recompute paths )
 					var tRestKeys2 setKey
-					if testing.Short() {
+					if !xbtreetest.VeryLong() {
 						tRestKeys2 = tAllKeys.Difference(keys1R2)
 					} else {
 						tRestKeys2 = tAllKeys.Difference(keys1)