diff --git a/aoc/src/run.rs b/aoc/src/run.rs
index 9394cfd..f99ed1b 100644
--- a/aoc/src/run.rs
+++ b/aoc/src/run.rs
@@ -1,6 +1,6 @@
 use chrono::{Datelike, Duration};
 use clap::Parser;
-use itertools::Itertools;
+use std::fmt::Write;
 
 #[derive(Parser)]
 #[clap(version, author)]
@@ -46,6 +46,44 @@ fn pretty_duration(duration: Duration) -> String {
     }
 }
 
+#[allow(clippy::module_name_repetitions)]
+pub fn run_tests<F>(
+    register: F,
+    single_day: Option<usize>,
+    main_only: bool,
+    timings: bool,
+) -> eyre::Result<String>
+where
+    F: Fn(),
+{
+    register();
+    let mut results = String::new();
+    let mut runners = super::runners::RUNNERS.lock().unwrap();
+    let keys = runners.keys().copied().collect::<Vec<_>>();
+    for (day, part) in keys {
+        if single_day.map_or(true, |d| d == day) {
+            for (version, runner) in runners.remove(&(day, part)).unwrap() {
+                if main_only && version.is_some() {
+                    continue;
+                }
+                write!(&mut results, "Day {day} - part {part}")?;
+                if let Some(version) = version {
+                    write!(&mut results, " — {version}")?;
+                }
+                let before = chrono::Utc::now();
+                let result = runner()?;
+                let after = chrono::Utc::now();
+                write!(&mut results, ": {result}")?;
+                if timings {
+                    write!(&mut results, " ({})", pretty_duration(after - before))?;
+                }
+                writeln!(&mut results)?;
+            }
+        }
+    }
+    Ok(results)
+}
+
 pub fn run<F>(register: F) -> eyre::Result<()>
 where
     F: Fn(),
@@ -62,35 +100,14 @@ where
         super::input::OVERRIDE_INPUT = opts.input;
     }
     let current_day = opts.day.unwrap_or(chrono::Utc::now().day() as usize);
-    register();
-    let mut runners = super::runners::RUNNERS.lock().unwrap();
-    let keys = runners.keys().copied().collect::<Vec<_>>();
-    for (day, part) in keys {
-        if day == current_day || opts.all {
-            for (version, runner) in runners.remove(&(day, part)).unwrap() {
-                if opts.main_only && version.is_some() {
-                    continue;
-                }
-                let before = chrono::Utc::now();
-                let result = runner();
-                let after = chrono::Utc::now();
-                let version = version
-                    .clone()
-                    .map_or_else(String::new, |v| format!(" — {v}"));
-                let elapsed = if opts.timing {
-                    format!(" ({})", pretty_duration(after - before))
-                } else {
-                    String::new()
-                };
-                let header = format!("Day {day} - part {part}{version}: ");
-                let sep = format!("\n{}", " ".repeat(header.len()));
-                let result = match result {
-                    Ok(e) => e.lines().join(&sep),
-                    Err(e) => format!("<error: {e:?}>"),
-                };
-                println!("{header}{result}{elapsed}");
-            }
-        }
-    }
+    println!(
+        "{}",
+        run_tests(
+            register,
+            (!opts.all).then_some(current_day),
+            opts.main_only,
+            opts.timing
+        )?
+    );
     Ok(())
 }
diff --git a/aoc/src/test.rs b/aoc/src/test.rs
index 2c8e66a..c6c42c1 100644
--- a/aoc/src/test.rs
+++ b/aoc/src/test.rs
@@ -4,14 +4,6 @@ use std::process::Command;
 
 const ENV_VAR: &str = "RECORD_RESULTS";
 
-fn run_with(args: &[&str]) -> eyre::Result<String> {
-    let output = Command::new("cargo")
-        .args(["run", "--release", "--", "-a"])
-        .args(args)
-        .output()?;
-    Ok(String::from_utf8(output.stdout)?)
-}
-
 fn equal_content<P: AsRef<Path>>(actual: &str, expected: P, show_diff: bool) -> eyre::Result<bool> {
     let expected_content = std::fs::read_to_string(expected.as_ref()).context(format!(
         "cannot read {}",
@@ -41,12 +33,12 @@ fn equal_content<P: AsRef<Path>>(actual: &str, expected: P, show_diff: bool) ->
     }
 }
 
-pub fn check_results<P: AsRef<Path>>(expected: P, main_only: bool) -> eyre::Result<bool> {
-    let actual = if main_only {
-        run_with(&["-m"])?
-    } else {
-        run_with(&[])?
-    };
+pub fn check_results<F: Fn(), P: AsRef<Path>>(
+    register: F,
+    expected: P,
+    main_only: bool,
+) -> eyre::Result<bool> {
+    let actual = super::run::run_tests(register, None, false, main_only)?;
     let update = std::env::var(ENV_VAR).is_ok();
     if update {
         if !matches!(equal_content(&actual, &expected, false), Ok(true)) {
diff --git a/aoc/tests/dummy-year.rs b/aoc/tests/dummy-year.rs
index 1be54ee..fb4f09d 100644
--- a/aoc/tests/dummy-year.rs
+++ b/aoc/tests/dummy-year.rs
@@ -65,21 +65,3 @@ fn all_days_main() {
     Day 2 - part 2: 3842356
     "###);
 }
-
-#[test]
-#[serial]
-fn check_expected_main() {
-    let dir = std::env::current_dir().unwrap();
-    std::env::set_current_dir("../dummy-year").unwrap();
-    assert!(aoc::test::check_results("expected.txt", true).unwrap());
-    std::env::set_current_dir(dir).unwrap();
-}
-
-#[test]
-#[serial]
-fn check_expected() {
-    let dir = std::env::current_dir().unwrap();
-    std::env::set_current_dir("../dummy-year").unwrap();
-    assert!(aoc::test::check_results("expected-all.txt", false).unwrap());
-    std::env::set_current_dir(dir).unwrap();
-}
diff --git a/dummy-year/expected-all.txt b/dummy-year/expected-all.txt
deleted file mode 100644
index d64c47f..0000000
--- a/dummy-year/expected-all.txt
+++ /dev/null
@@ -1,7 +0,0 @@
-Day 1 - part 1: 232
-Day 1 - part 1 — str_slice: 232
-Day 1 - part 2: 1783
-Day 1 - part 2 — result: 1783
-Day 1 - part 2 — result_string: 1783
-Day 2 - part 1: 1606483
-Day 2 - part 2: 3842356
diff --git a/dummy-year/expected.txt b/dummy-year/expected.txt
index 0ee80ec..d64c47f 100644
--- a/dummy-year/expected.txt
+++ b/dummy-year/expected.txt
@@ -1,4 +1,7 @@
 Day 1 - part 1: 232
+Day 1 - part 1 — str_slice: 232
 Day 1 - part 2: 1783
+Day 1 - part 2 — result: 1783
+Day 1 - part 2 — result_string: 1783
 Day 2 - part 1: 1606483
 Day 2 - part 2: 3842356
diff --git a/dummy-year/src/day1.rs b/dummy-year/src/day1.rs
index 38b5f8b..a57410c 100644
--- a/dummy-year/src/day1.rs
+++ b/dummy-year/src/day1.rs
@@ -7,7 +7,7 @@ fn part1(input: &str) -> usize {
 
 #[aoc(day1, part1, str_slice)]
 fn part1_string_slice(input: &[&str]) -> usize {
-    input.iter().cloned().map(part1).sum()
+    input.iter().copied().map(part1).sum()
 }
 
 #[aoc(day1, part2)]
diff --git a/dummy-year/tests/check-expected.rs b/dummy-year/tests/check-expected.rs
new file mode 100644
index 0000000..7019b81
--- /dev/null
+++ b/dummy-year/tests/check-expected.rs
@@ -0,0 +1,9 @@
+#[test]
+fn check_expected() {
+    assert!(aoc::test::check_results(
+        dummy_year::register::register_runners,
+        "expected.txt",
+        false
+    )
+    .unwrap());
+}