speed up the integration test for branch lengths

Author: molpopgen

examples/haploid_wright_fisher.rs

@@ -114,7 +114,7 @@ proptest! {
 #[test]
     fn test_simulate_proptest(seed in any::<u64>(),
                               num_generations in 50..100i32,
-                              simplify_interval in 1..100i32 ) {
+                              simplify_interval in 1..100i32) {
         let ts = simulate(seed, 100, num_generations, simplify_interval).unwrap();
 
         // stress test the branch length fn b/c it is not a trivial
@@ -123,7 +123,8 @@ proptest! {
             use streaming_iterator::StreamingIterator;
             let mut x = f64::NAN;
             if let Ok(mut tree_iter) = ts.tree_iterator(0) {
-                while let Some(tree) = tree_iter.next() {
+                // We will only do the first tree to save time.
+                if let Some(tree) = tree_iter.next() {
                     let b = tree.total_branch_length(false).unwrap();
                     let b2 = unsafe {
                         tskit::bindings::tsk_tree_get_total_branch_length(tree.as_ptr(), -1, &mut x)