Enhance pmt_tests execution time

pmt_tests with different tx counts were  executed in a single test, not taking advantage of the parallelism provided by unit tests.
A macro was added to define a unit test per transaction count.

src/util/merkleblock.rs

@@ -532,22 +532,36 @@ mod tests {
     use crate::util::merkleblock::{MerkleBlock, PartialMerkleTree};
     use crate::Block;
 
-    #[test]
-    fn pmt_tests() {
-        let mut rng = thread_rng();
-        let tx_counts = vec![1, 4, 7, 17, 56, 100, 127, 256, 312, 513, 1000, 4095];
+    /// accepts `pmt_test_$num`
+    fn pmt_test_from_name(name: &str) {
+        pmt_test(name[9..].parse().unwrap())
+    }
 
-        for num_tx in tx_counts {
+    macro_rules! pmt_tests {
+    ($($name:ident),* $(,)?) => {
+         $(
+        #[test]
+        fn $name() {
+            pmt_test_from_name(stringify!($name));
+        }
+         )*
+    }
+}
+    pmt_tests!(pmt_test_1, pmt_test_4, pmt_test_7, pmt_test_17, pmt_test_56, pmt_test_100,
+        pmt_test_127, pmt_test_256, pmt_test_312, pmt_test_513, pmt_test_1000, pmt_test_4095);
+
+    fn pmt_test(tx_count: usize) {
+        let mut rng = thread_rng();
         // Create some fake tx ids
-            let txids = (1..num_tx + 1) // change to `1..=num_tx` when min Rust >= 1.26.0
+        let tx_ids = (1..=tx_count)
             .map(|i| Txid::from_hex(&format!("{:064x}", i)).unwrap())
             .collect::<Vec<_>>();
 
         // Calculate the merkle root and height
-            let hashes = txids.iter().map(|t| t.as_hash());
+        let hashes = tx_ids.iter().map(|t| t.as_hash());
         let merkle_root_1: TxMerkleNode = bitcoin_merkle_root(hashes).expect("hashes is not empty").into();
         let mut height = 1;
-            let mut ntx = num_tx;
+        let mut ntx = tx_count;
         while ntx > 1 {
             ntx = (ntx + 1) / 2;
             height += 1;
@@ -555,9 +569,9 @@ mod tests {
 
         // Check with random subsets with inclusion chances 1, 1/2, 1/4, ..., 1/128
         for att in 1..15 {
-                let mut matches = vec![false; num_tx];
+            let mut matches = vec![false; tx_count];
             let mut match_txid1 = vec![];
-                for j in 0..num_tx {
+            for j in 0..tx_count {
                 // Generate `att / 2` random bits
                 let rand_bits = match att / 2 {
                     0 => 0,
@@ -567,16 +581,16 @@ mod tests {
                 matches[j] = include;
 
                 if include {
-                        match_txid1.push(txids[j]);
+                    match_txid1.push(tx_ids[j]);
                 };
             }
 
             // Build the partial merkle tree
-                let pmt1 = PartialMerkleTree::from_txids(&txids, &matches);
+            let pmt1 = PartialMerkleTree::from_txids(&tx_ids, &matches);
             let serialized = serialize(&pmt1);
 
             // Verify PartialMerkleTree's size guarantees
-                let n = min(num_tx, 1 + match_txid1.len() * height);
+            let n = min(tx_count, 1 + match_txid1.len() * height);
             assert!(serialized.len() <= 10 + (258 * n + 7) / 8);
 
             // Deserialize into a tester copy
@@ -609,7 +623,6 @@ mod tests {
             }
         }
     }
-    }
 
     #[test]
     fn pmt_malleability() {