Support matrices of independent parameter lists

This patch permits the `-L`/`--parameter-list` argument to appear
multiple times. Each additional parameter increases the dimensionality
of the parameter matrix. One benchmark will be run for each combination
of parameters (i.e., the benchmark space is the Cartesian product of the
parameter spaces).

For now, `--parameter-list` and `--parameter-scan` are still mutually
exclusive. If desired, a follow-up change could similarly permit
multiple occurrences of `--parameter-scan` and also permit use of both
listed and scanned parameters together. (After all, `--parameter-scan`
can be thought of as syntactic sugar for a parameter list.)

This implementation is a little profligate with memory usage for
`BenchmarkResult`s: each result contains a separate copy of all
parameter names (as `String`s). This could be done away with by
threading lifetimes through the `BenchmarkResult`s, or by ref-counting
the names.

Because `BenchmarkResult`s now have maps with arbitrary key sets, we can
no longer use `serde` to serialize them to CSV. But a CSV writer is easy
to write by hand, so we just do that.

Fixes #253.

Test Plan:
Some unit tests included. As an integration test, try:

```
cargo run --release -- --runs 10 \
    -L foo foo1,foo2 -L bar bar9,bar8 \
    'echo {foo} {bar}' \
    'printf "%s\n" {foo} {bar}' \
    --export-csv /tmp/out
```

with all the export formats.

wchargin-branch: param-list-matrix
wchargin-source: 11051ab222c9de0fbc6ac6a080fbca48e05996c2

src/hyperfine/app.rs

@@ -3,9 +3,10 @@ use atty::Stream;
 use clap::{crate_version, App, AppSettings, Arg, ArgMatches};
 use std::ffi::OsString;
 
-pub fn get_arg_matches<T>(args: T) -> ArgMatches<'static>
+pub fn get_arg_matches<I, T>(args: I) -> ArgMatches<'static>
 where
-    T: Iterator<Item = OsString>,
+    I: IntoIterator<Item = T>,
+    T: Into<OsString> + Clone,
 {
     let app = build_app();
     app.get_matches_from(args)
@@ -134,6 +135,7 @@ fn build_app() -> App<'static, 'static> {
                 .long("parameter-list")
                 .short("L")
                 .takes_value(true)
+                .multiple(true)
                 .allow_hyphen_values(true)
                 .value_names(&["VAR", "VALUES"])
                 .conflicts_with_all(&["parameter-scan", "parameter-step-size"])

src/hyperfine/benchmark.rs

@@ -223,12 +223,7 @@ pub fn run_benchmark(
         } else {
             &values[num]
         };
-        match cmd.get_parameter() {
-            Some((param, value)) => {
-                Command::new_parametrized(preparation_command, param, value.clone())
-            }
-            None => Command::new(preparation_command),
-        }
+        Command::new_parametrized(preparation_command, cmd.get_parameters().clone())
     });
 
     // Warmup phase
@@ -414,16 +409,9 @@ pub fn run_benchmark(
     }
 
     // Run cleanup command
-    let cleanup_cmd =
-        options
-            .cleanup_command
-            .as_ref()
-            .map(|cleanup_command| match cmd.get_parameter() {
-                Some((param, value)) => {
-                    Command::new_parametrized(cleanup_command, param, value.clone())
-                }
-                None => Command::new(cleanup_command),
-            });
+    let cleanup_cmd = options.cleanup_command.as_ref().map(|cleanup_command| {
+        Command::new_parametrized(cleanup_command, cmd.get_parameters().clone())
+    });
     run_cleanup_command(&options.shell, &cleanup_cmd, options.show_output)?;
 
     Ok(BenchmarkResult::new(
@@ -436,6 +424,9 @@ pub fn run_benchmark(
         t_min,
         t_max,
         times_real,
-        cmd.get_parameter().as_ref().map(|p| p.1.to_string()),
+        cmd.get_parameters()
+            .iter()
+            .map(|(name, value)| ((*name).to_string(), value.to_string()))
+            .collect(),
     ))
 }

src/hyperfine/export/asciidoc.rs

@@ -83,6 +83,7 @@ fn test_asciidoc_header() {
 /// Ensure each table row is generated properly
 #[test]
 fn test_asciidoc_table_row() {
+    use std::collections::BTreeMap;
     let result = BenchmarkResult::new(
         String::from("sleep 1"), // command
         0.10491992406666667,     // mean
@@ -98,7 +99,7 @@ fn test_asciidoc_table_row() {
             0.10745223440000001,
             0.10697327940000001,
         ],
-        None, // param
+        BTreeMap::new(), // param
     );
 
     let expms = format!(
@@ -134,6 +135,7 @@ fn test_asciidoc_table_row() {
 /// Ensure commands get properly escaped
 #[test]
 fn test_asciidoc_table_row_command_escape() {
+    use std::collections::BTreeMap;
     let result = BenchmarkResult::new(
         String::from("sleep 1|"), // command
         0.10491992406666667,      // mean
@@ -149,7 +151,7 @@ fn test_asciidoc_table_row_command_escape() {
             0.10745223440000001,
             0.10697327940000001,
         ],
-        None, // param
+        BTreeMap::new(), // param
     );
     let exps = format!(
         "| `sleep 1\\|`\n\
@@ -169,11 +171,12 @@ fn test_asciidoc_table_row_command_escape() {
 /// Integration test
 #[test]
 fn test_asciidoc() {
+    use std::collections::BTreeMap;
     let exporter = AsciidocExporter::default();
     // NOTE: results are fabricated, unlike above
     let results = vec![
         BenchmarkResult::new(
-            String::from("command | 1"),
+            String::from("FOO=1 BAR=2 command | 1"),
             1.0,
             2.0,
             1.0,
@@ -182,10 +185,15 @@ fn test_asciidoc() {
             5.0,
             6.0,
             vec![7.0, 8.0, 9.0],
-            None,
+            {
+                let mut params = BTreeMap::new();
+                params.insert("foo".into(), "1".into());
+                params.insert("bar".into(), "2".into());
+                params
+            },
         ),
         BenchmarkResult::new(
-            String::from("command | 2"),
+            String::from("FOO=1 BAR=7 command | 2"),
             11.0,
             12.0,
             11.0,
@@ -194,7 +202,12 @@ fn test_asciidoc() {
             15.0,
             16.0,
             vec![17.0, 18.0, 19.0],
-            None,
+            {
+                let mut params = BTreeMap::new();
+                params.insert("foo".into(), "1".into());
+                params.insert("bar".into(), "7".into());
+                params
+            },
         ),
     ];
     // NOTE: only testing with s, s/ms is tested elsewhere
@@ -203,11 +216,11 @@ fn test_asciidoc() {
          |===\n\
          | Command | Mean [s] | Min…Max [s]\n\
          \n\
-         | `command \\| 1`\n\
+         | `FOO=1 BAR=2 command \\| 1`\n\
          | 1.000 ± 2.000\n\
          | 5.000…6.000\n\
          \n\
-         | `command \\| 2`\n\
+         | `FOO=1 BAR=7 command \\| 2`\n\
          | 11.000 ± 12.000\n\
          | 15.000…16.000\n\
          |===\n\

src/hyperfine/export/csv.rs

@@ -3,6 +3,7 @@ use super::Exporter;
 use crate::hyperfine::types::BenchmarkResult;
 use crate::hyperfine::units::Unit;
 
+use std::borrow::Cow;
 use std::io::{Error, ErrorKind, Result};
 
 use csv::WriterBuilder;
@@ -13,12 +14,35 @@ pub struct CsvExporter {}
 impl Exporter for CsvExporter {
     fn serialize(&self, results: &[BenchmarkResult], _unit: Option<Unit>) -> Result<Vec<u8>> {
         let mut writer = WriterBuilder::new().from_writer(vec![]);
-        for res in results {
-            // The list of times cannot be exported to the CSV file - remove it:
-            let mut result = res.clone();
-            result.times = None;
 
-            writer.serialize(result)?;
+        {
+            let mut headers: Vec<String> = [
+                // The list of times cannot be exported to the CSV file - omit it.
+                "command", "mean", "stddev", "median", "user", "system", "min", "max",
+            ]
+            .iter()
+            .map(|x| (*x).to_string())
+            .collect();
+            if let Some(res) = results.first() {
+                for param_name in res.parameters.keys() {
+                    headers.push(format!("parameter_{}", param_name));
+                }
+            }
+            writer.write_record(headers)?;
+        }
+
+        for res in results {
+            let mut fields = Vec::new();
+            fields.push(Cow::Borrowed(res.command.as_bytes()));
+            for f in &[
+                res.mean, res.stddev, res.median, res.user, res.system, res.min, res.max,
+            ] {
+                fields.push(Cow::Owned(f.to_string().into_bytes()))
+            }
+            for v in res.parameters.values() {
+                fields.push(Cow::Borrowed(v.as_bytes()))
+            }
+            writer.write_record(fields)?;
         }
 
         writer
@@ -26,3 +50,57 @@ impl Exporter for CsvExporter {
             .map_err(|e| Error::new(ErrorKind::Other, e))
     }
 }
+
+#[test]
+fn test_csv() {
+    use std::collections::BTreeMap;
+    let exporter = CsvExporter::default();
+
+    // NOTE: results are fabricated
+    let results = vec![
+        BenchmarkResult::new(
+            String::from("FOO=one BAR=two command | 1"),
+            1.0,
+            2.0,
+            1.0,
+            3.0,
+            4.0,
+            5.0,
+            6.0,
+            vec![7.0, 8.0, 9.0],
+            {
+                let mut params = BTreeMap::new();
+                params.insert("foo".into(), "one".into());
+                params.insert("bar".into(), "two".into());
+                params
+            },
+        ),
+        BenchmarkResult::new(
+            String::from("FOO=one BAR=seven command | 2"),
+            11.0,
+            12.0,
+            11.0,
+            13.0,
+            14.0,
+            15.0,
+            16.5,
+            vec![17.0, 18.0, 19.0],
+            {
+                let mut params = BTreeMap::new();
+                params.insert("foo".into(), "one".into());
+                params.insert("bar".into(), "seven".into());
+                params
+            },
+        ),
+    ];
+    let exps: String = String::from(
+        "command,mean,stddev,median,user,system,min,max,parameter_bar,parameter_foo\n\
+        FOO=one BAR=two command | 1,1,2,1,3,4,5,6,two,one\n\
+        FOO=one BAR=seven command | 2,11,12,11,13,14,15,16.5,seven,one\n\
+        ",
+    );
+    let gens =
+        String::from_utf8(exporter.serialize(&results, Some(Unit::Second)).unwrap()).unwrap();
+
+    assert_eq!(exps, gens);
+}

src/hyperfine/export/markdown.rs

@@ -82,6 +82,7 @@ fn add_table_row(dest: &mut Vec<u8>, entry: &BenchmarkResultWithRelativeSpeed, u
 /// the units for all entries when the time unit is not given.
 #[test]
 fn test_markdown_format_ms() {
+    use std::collections::BTreeMap;
     let exporter = MarkdownExporter::default();
 
     let mut timing_results = vec![];
@@ -96,7 +97,7 @@ fn test_markdown_format_ms() {
         0.1023,              // min
         0.1080,              // max
         vec![0.1, 0.1, 0.1], // times
-        None,                // parameter
+        BTreeMap::new(),     // parameter
     ));
 
     timing_results.push(BenchmarkResult::new(
@@ -109,7 +110,7 @@ fn test_markdown_format_ms() {
         2.0020,              // min
         2.0080,              // max
         vec![2.0, 2.0, 2.0], // times
-        None,                // parameter
+        BTreeMap::new(),     // parameter
     ));
 
     let formatted = String::from_utf8(exporter.serialize(&timing_results, None).unwrap()).unwrap();
@@ -129,6 +130,7 @@ fn test_markdown_format_ms() {
 /// the units for all entries when the time unit is not given.
 #[test]
 fn test_markdown_format_s() {
+    use std::collections::BTreeMap;
     let exporter = MarkdownExporter::default();
 
     let mut timing_results = vec![];
@@ -143,7 +145,7 @@ fn test_markdown_format_s() {
         2.0020,              // min
         2.0080,              // max
         vec![2.0, 2.0, 2.0], // times
-        None,                // parameter
+        BTreeMap::new(),     // parameter
     ));
 
     timing_results.push(BenchmarkResult::new(
@@ -156,7 +158,7 @@ fn test_markdown_format_s() {
         0.1023,              // min
         0.1080,              // max
         vec![0.1, 0.1, 0.1], // times
-        None,                // parameter
+        BTreeMap::new(),     // parameter
     ));
 
     let formatted = String::from_utf8(exporter.serialize(&timing_results, None).unwrap()).unwrap();
@@ -175,6 +177,7 @@ fn test_markdown_format_s() {
 /// The given time unit (s) is used to set the units for all entries.
 #[test]
 fn test_markdown_format_time_unit_s() {
+    use std::collections::BTreeMap;
     let exporter = MarkdownExporter::default();
 
     let mut timing_results = vec![];
@@ -189,7 +192,7 @@ fn test_markdown_format_time_unit_s() {
         0.1023,              // min
         0.1080,              // max
         vec![0.1, 0.1, 0.1], // times
-        None,                // parameter
+        BTreeMap::new(),     // parameter
     ));
 
     timing_results.push(BenchmarkResult::new(
@@ -202,7 +205,7 @@ fn test_markdown_format_time_unit_s() {
         2.0020,              // min
         2.0080,              // max
         vec![2.0, 2.0, 2.0], // times
-        None,                // parameter
+        BTreeMap::new(),     // parameter
     ));
 
     let formatted = String::from_utf8(
@@ -227,6 +230,7 @@ fn test_markdown_format_time_unit_s() {
 /// the units for all entries.
 #[test]
 fn test_markdown_format_time_unit_ms() {
+    use std::collections::BTreeMap;
     let exporter = MarkdownExporter::default();
 
     let mut timing_results = vec![];
@@ -241,7 +245,7 @@ fn test_markdown_format_time_unit_ms() {
         2.0020,              // min
         2.0080,              // max
         vec![2.0, 2.0, 2.0], // times
-        None,                // parameter
+        BTreeMap::new(),     // parameter
     ));
 
     timing_results.push(BenchmarkResult::new(
@@ -254,7 +258,7 @@ fn test_markdown_format_time_unit_ms() {
         0.1023,              // min
         0.1080,              // max
         vec![0.1, 0.1, 0.1], // times
-        None,                // parameter
+        BTreeMap::new(),     // parameter
     ));
 
     let formatted = String::from_utf8(

src/hyperfine/internal.rs

@@ -128,6 +128,7 @@ fn test_max() {
 #[test]
 fn test_compute_relative_speed() {
     use approx::assert_relative_eq;
+    use std::collections::BTreeMap;
 
     let create_result = |name: &str, mean| BenchmarkResult {
         command: name.into(),
@@ -139,7 +140,7 @@ fn test_compute_relative_speed() {
         min: mean,
         max: mean,
         times: None,
-        parameter: None,
+        parameters: BTreeMap::new(),
     };
 
     let results = vec![

src/hyperfine/parameter_range.rs

@@ -94,8 +94,7 @@ fn build_parameterized_commands<'a, T: Numeric>(
         for cmd in &command_strings {
             commands.push(Command::new_parametrized(
                 cmd,
-                param_name,
-                ParameterValue::Numeric(value.into()),
+                vec![(param_name, ParameterValue::Numeric(value.into()))],
             ));
         }
     }

src/hyperfine/types.rs

@@ -1,6 +1,7 @@
 use rust_decimal::Decimal;
 /// This module contains common internal types.
 use serde::*;
+use std::collections::BTreeMap;
 use std::fmt;
 
 use crate::hyperfine::units::{Second, Unit};
@@ -11,7 +12,7 @@ pub const DEFAULT_SHELL: &str = "sh";
 #[cfg(windows)]
 pub const DEFAULT_SHELL: &str = "cmd.exe";
 
-#[derive(Debug, Clone, Serialize, Copy, PartialEq)]
+#[derive(Debug, Clone, Serialize, Copy, PartialEq, Eq)]
 #[serde(untagged)]
 pub enum NumericType {
     Int(i32),
@@ -39,7 +40,7 @@ impl Into<NumericType> for Decimal {
     }
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum ParameterValue {
     Text(String),
     Numeric(NumericType),
@@ -55,49 +56,79 @@ impl<'a> ToString for ParameterValue {
 }
 
 /// A command that should be benchmarked.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Command<'a> {
     /// The command that should be executed (without parameter substitution)
     expression: &'a str,
 
-    /// A possible parameter value.
-    parameter: Option<(&'a str, ParameterValue)>,
+    /// Zero or more parameter values.
+    parameters: Vec<(&'a str, ParameterValue)>,
 }
 
 impl<'a> Command<'a> {
     pub fn new(expression: &'a str) -> Command<'a> {
         Command {
             expression,
-            parameter: None,
+            parameters: Vec::new(),
         }
     }
 
     pub fn new_parametrized(
         expression: &'a str,
-        parameter: &'a str,
-        value: ParameterValue,
+        parameters: Vec<(&'a str, ParameterValue)>,
     ) -> Command<'a> {
         Command {
             expression,
-            parameter: Some((parameter, value)),
+            parameters,
         }
     }
 
     pub fn get_shell_command(&self) -> String {
-        match &self.parameter {
-            Some((param_name, param_value)) => self.expression.replace(
-                &format!("{{{param_name}}}", param_name = param_name),
-                &param_value.to_string(),
-            ),
-            None => self.expression.into(),
+        let mut result = String::new();
+        let mut replacements = BTreeMap::<String, String>::new();
+        for (param_name, param_value) in &self.parameters {
+            replacements.insert(
+                format!("{{{param_name}}}", param_name = param_name),
+                param_value.to_string(),
+            );
         }
+        let mut remaining = self.expression;
+        // Manually replace consecutive occurrences to avoid double-replacing: e.g.,
+        //
+        //     hyperfine -L foo 'a,{bar}' -L bar 'baz,quux' 'echo {foo} {bar}'
+        //
+        // should not ever run 'echo baz baz'. See `test_get_shell_command_nonoverlapping`.
+        'outer: while let Some(head) = remaining.chars().next() {
+            for (k, v) in &replacements {
+                if remaining.starts_with(k.as_str()) {
+                    result.push_str(&v);
+                    remaining = &remaining[k.len()..];
+                    continue 'outer;
+                }
+            }
+            result.push(head);
+            remaining = &remaining[head.len_utf8()..];
+        }
+        result
     }
 
-    pub fn get_parameter(&self) -> &Option<(&'a str, ParameterValue)> {
-        &self.parameter
+    pub fn get_parameters(&self) -> &Vec<(&'a str, ParameterValue)> {
+        &self.parameters
     }
 }
 
+#[test]
+fn test_get_shell_command_nonoverlapping() {
+    let cmd = Command::new_parametrized(
+        "echo {foo} {bar}",
+        vec![
+            ("foo", ParameterValue::Text("{bar} baz".into())),
+            ("bar", ParameterValue::Text("quux".into())),
+        ],
+    );
+    assert_eq!(cmd.get_shell_command(), "echo {bar} baz quux");
+}
+
 impl<'a> fmt::Display for Command<'a> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "{}", self.get_shell_command())
@@ -199,6 +230,8 @@ impl Default for HyperfineOptions {
 }
 
 /// Set of values that will be exported.
+// NOTE: `serde` is used for JSON serialization, but not for CSV serialization due to the
+// `parameters` map. Update `src/hyperfine/export/csv.rs` with new fields, as appropriate.
 #[derive(Debug, Default, Clone, Serialize, PartialEq)]
 pub struct BenchmarkResult {
     /// The command that was run
@@ -229,9 +262,9 @@ pub struct BenchmarkResult {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub times: Option<Vec<Second>>,
 
-    /// Any parameter used
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub parameter: Option<String>,
+    /// Any parameter values used
+    #[serde(skip_serializing_if = "BTreeMap::is_empty")]
+    pub parameters: BTreeMap<String, String>,
 }
 
 impl BenchmarkResult {
@@ -246,7 +279,7 @@ impl BenchmarkResult {
         min: Second,
         max: Second,
         times: Vec<Second>,
-        parameter: Option<String>,
+        parameters: BTreeMap<String, String>,
     ) -> Self {
         BenchmarkResult {
             command,
@@ -258,7 +291,7 @@ impl BenchmarkResult {
             min,
             max,
             times: Some(times),
-            parameter,
+            parameters,
         }
     }
 }

src/main.rs

@@ -1,4 +1,5 @@
 use std::cmp;
+use std::collections::BTreeMap;
 use std::env;
 use std::io;
 
@@ -207,23 +208,60 @@ fn build_commands<'a>(matches: &'a ArgMatches<'_>) -> Vec<Command<'a>> {
             Ok(commands) => commands,
             Err(e) => error(&e.to_string()),
         }
-    } else if let Some(mut args) = matches.values_of("parameter-list") {
-        let param_name = args.next().unwrap();
-        let param_list_str = args.next().unwrap();
-
-        let param_list = tokenize(param_list_str);
+    } else if let Some(args) = matches.values_of("parameter-list") {
+        let args: Vec<_> = args.collect();
+        let param_names_and_values: Vec<(&str, Vec<String>)> = args
+            .chunks_exact(2)
+            .map(|pair| {
+                let name = pair[0];
+                let list_str = pair[1];
+                (name, tokenize(list_str))
+            })
+            .collect();
+        {
+            let dupes = find_dupes(param_names_and_values.iter().map(|(name, _)| *name));
+            if !dupes.is_empty() {
+                error(&format!("duplicate parameter names: {}", &dupes.join(", ")))
+            }
+        }
         let command_list = command_strings.collect::<Vec<&str>>();
 
-        let mut commands = Vec::with_capacity(param_list.len() * command_list.len());
+        let dimensions: Vec<usize> = std::iter::once(command_list.len())
+            .chain(
+                param_names_and_values
+                    .iter()
+                    .map(|(_, values)| values.len()),
+            )
+            .collect();
+        let param_space_size = dimensions.iter().product();
+        if param_space_size == 0 {
+            return Vec::new();
+        }
 
-        for value in param_list {
-            for cmd in &command_list {
-                commands.push(Command::new_parametrized(
-                    cmd,
-                    param_name,
-                    ParameterValue::Text(value.clone()),
-                ));
+        let mut commands = Vec::with_capacity(param_space_size);
+        let mut index = vec![0usize; dimensions.len()];
+        'outer: loop {
+            let (command_index, params_indices) = index.split_first().unwrap();
+            let parameters = param_names_and_values
+                .iter()
+                .zip(params_indices)
+                .map(|((name, values), i)| (*name, ParameterValue::Text(values[*i].clone())))
+                .collect();
+            commands.push(Command::new_parametrized(
+                command_list[*command_index],
+                parameters,
+            ));
+
+            // Increment index, exiting loop on overflow.
+            for (i, n) in index.iter_mut().zip(dimensions.iter()) {
+                *i += 1;
+                if *i < *n {
+                    continue 'outer;
+                } else {
+                    *i = 0;
+                }
             }
+            break 'outer;
         }
 
         commands
@@ -231,3 +269,52 @@ fn build_commands<'a>(matches: &'a ArgMatches<'_>) -> Vec<Command<'a>> {
         command_strings.map(Command::new).collect()
     }
 }
+
+/// Finds all the strings that appear multiple times in the input iterator, returning them in
+/// sorted order. If no string appears more than once, the result is an empty vector.
+fn find_dupes<'a, I: IntoIterator<Item = &'a str>>(i: I) -> Vec<&'a str> {
+    let mut counts = BTreeMap::<&'a str, usize>::new();
+    for s in i {
+        *counts.entry(s).or_default() += 1;
+    }
+    counts
+        .into_iter()
+        .filter_map(|(k, n)| if n > 1 { Some(k) } else { None })
+        .collect()
+}
+
+#[test]
+fn test_build_commands_cross_product() {
+    let matches = get_arg_matches(vec![
+        "hyperfine",
+        "-L",
+        "foo",
+        "a,b",
+        "-L",
+        "bar",
+        "z,y",
+        "echo {foo} {bar}",
+        "printf '%s\n' {foo} {bar}",
+    ]);
+    let result = build_commands(&matches);
+
+    // Iteration order: command list first, then parameters in listed order (here, "foo" before
+    // "bar", which is distinct from their sorted order), with parameter values in listed order.
+    let pv = |s: &str| ParameterValue::Text(s.to_string());
+    let cmd = |cmd: usize, foo: &str, bar: &str| {
+        let expression = ["echo {foo} {bar}", "printf '%s\n' {foo} {bar}"][cmd];
+        let params = vec![("foo", pv(foo)), ("bar", pv(bar))];
+        Command::new_parametrized(expression, params)
+    };
+    let expected = vec![
+        cmd(0, "a", "z"),
+        cmd(1, "a", "z"),
+        cmd(0, "b", "z"),
+        cmd(1, "b", "z"),
+        cmd(0, "a", "y"),
+        cmd(1, "a", "y"),
+        cmd(0, "b", "y"),
+        cmd(1, "b", "y"),
+    ];
+    assert_eq!(result, expected);
+}