print how much time all tests took

docs/design/maps.md

@@ -260,6 +260,7 @@ it?
 I thought I had a list of these somewhere else?
 
 - min length for lanes, turns
+- length for related lanes (sidewalk spot / parking / driving) matching up
 - connectivity
 - no loop lanes (same src and dst endpt)... but what about cul-de-sacs then?
 

tests/src/runner.rs

@@ -34,6 +34,7 @@ pub struct TestRunner {
     results: Vec<TestResult>,
     flags: Flags,
     output_dir: String,
+    started_at: std::time::Instant,
 }
 
 struct TestResult {
@@ -95,6 +96,7 @@ impl TestRunner {
                     .unwrap()
                     .as_secs()
             ),
+            started_at: std::time::Instant::now(),
         }
     }
 
@@ -192,7 +194,12 @@ impl TestRunner {
             }
         }
 
-        println!("\n{} tests passed, {} tests failed", passed, failed);
+        println!(
+            "\n{} tests passed, {} tests failed in {:.02}s",
+            passed,
+            failed,
+            abstutil::elapsed_seconds(self.started_at)
+        );
     }
 }