Fix prepare and conclude behaviour and add tests.

src/benchmark/relative_speed.rs

@@ -155,6 +155,20 @@ fn test_compute_relative_speed() {
     assert_relative_eq!(2.5, annotated_results[2].relative_speed);
 }
 
+#[test]
+fn test_compute_relative_speed_with_reference() {
+    use approx::assert_relative_eq;
+
+    let results = vec![create_result("cmd2", 2.0), create_result("cmd3", 5.0)];
+    let reference = create_result("cmd2", 4.0);
+
+    let annotated_results =
+        compute_with_check_from_reference(&results, &reference, SortOrder::Command).unwrap();
+
+    assert_relative_eq!(2.0, annotated_results[0].relative_speed);
+    assert_relative_eq!(1.25, annotated_results[1].relative_speed);
+}
+
 #[test]
 fn test_compute_relative_speed_for_zero_times() {
     let results = vec![create_result("cmd1", 1.0), create_result("cmd2", 0.0)];

src/options.rs

@@ -437,21 +437,25 @@ impl Options {
     }
 
     pub fn validate_against_command_list(&self, commands: &Commands) -> Result<()> {
+        let num_commands = commands.num_commands()
+            + if self.reference_command.is_some() {
+                1
+            } else {
+                0
+            };
         if let Some(preparation_command) = &self.preparation_command {
             ensure!(
-                preparation_command.len() <= 1
-                    || commands.num_commands() == preparation_command.len(),
+                preparation_command.len() <= 1 || num_commands == preparation_command.len(),
                 "The '--prepare' option has to be provided just once or N times, where N is the \
-             number of benchmark commands."
+             number of benchmark commands including a potential reference."
             );
         }
 
         if let Some(conclusion_command) = &self.conclusion_command {
             ensure!(
-                conclusion_command.len() <= 1
-                    || commands.num_commands() == conclusion_command.len(),
+                conclusion_command.len() <= 1 || num_commands == conclusion_command.len(),
                 "The '--conclude' option has to be provided just once or N times, where N is the \
-             number of benchmark commands."
+             number of benchmark commands including a potential reference."
             );
         }