Add unit test for calc_tree_width

Add a unit test for a `PartialMerkleTree` with node counts of 1-7

bitcoin/src/merkle_tree/block.rs

@@ -767,4 +767,54 @@ mod tests {
         let block_hex = include_str!("../../tests/data/block_13b8a.hex");
         deserialize(&Vec::from_hex(block_hex).unwrap()).unwrap()
     }
+
+    macro_rules! check_calc_tree_width {
+        ($($test_name:ident, $num_transactions:literal, $height:literal, $expected_width:literal);* $(;)?) => {
+            $(
+                #[test]
+                fn $test_name() {
+                    let pmt = PartialMerkleTree {
+                        num_transactions: $num_transactions,
+                        bits: vec![],
+                        hashes: vec![],
+                    };
+                    let got = pmt.calc_tree_width($height);
+                    assert_eq!(got, $expected_width)
+                }
+            )*
+        }
+    }
+
+    // tree_width_<id> <num txs> <height> <expected_width>
+    //
+    // height 0 is the bottom of the tree, where the leaves are.
+    check_calc_tree_width! {
+        tree_width_01, 1, 0, 1;
+        //
+        tree_width_02, 2, 0, 2;
+        tree_width_03, 2, 1, 1;
+        //
+        tree_width_04, 3, 0, 3;
+        tree_width_05, 3, 1, 2;
+        tree_width_06, 3, 2, 1;
+        //
+        tree_width_07, 4, 0, 4;
+        tree_width_08, 4, 1, 2;
+        tree_width_09, 4, 2, 1;
+        //
+        tree_width_10, 5, 0, 5;
+        tree_width_11, 5, 1, 3;
+        tree_width_12, 5, 2, 2;
+        tree_width_13, 5, 3, 1;
+        //
+        tree_width_14, 6, 0, 6;
+        tree_width_15, 6, 1, 3;
+        tree_width_16, 6, 2, 2;
+        tree_width_17, 6, 3, 1;
+        //
+        tree_width_18, 7, 0, 7;
+        tree_width_19, 7, 1, 4;
+        tree_width_20, 7, 2, 2;
+        tree_width_21, 7, 3, 1;
+    }
 }