diff --git a/tests/common/mod.rs b/tests/common/mod.rs
index a8a275919..bad0647d6 100644
--- a/tests/common/mod.rs
+++ b/tests/common/mod.rs
@@ -222,13 +222,3 @@ pub fn create_conda_env(name: &str, major: usize, minor: usize) -> Result<(PathB
 pub fn test_python_path() -> Option<String> {
     env::var("MATURIN_TEST_PYTHON").ok()
 }
-
-/// Find index of subslice in a larger slice
-pub fn find_subslice<T: PartialEq>(haystack: &[T], needle: &[T]) -> Option<usize> {
-    if needle.is_empty() {
-        return Some(0);
-    }
-    haystack
-        .windows(needle.len())
-        .position(|window| window == needle)
-}
diff --git a/tests/common/pep517.rs b/tests/common/pep517.rs
index c5d8f951d..4f826b7f7 100644
--- a/tests/common/pep517.rs
+++ b/tests/common/pep517.rs
@@ -4,6 +4,13 @@ use std::path::{Path, PathBuf};
 use std::process::{Command, Output};
 use std::str;
 
+pub fn target_dir(unique_name: &str) -> String {
+    format!(
+        "{}/test-crates/targets/{unique_name}",
+        env!("CARGO_MANIFEST_DIR")
+    )
+}
+
 /// Creates a virtualenv and activates it, checks that the package isn't installed, uses
 /// pip install to install it and checks it is working
 pub fn test_pep517(
@@ -47,13 +54,8 @@ pub fn test_pep517(
 
     cmd.arg(package.to_str().expect("package is utf8 path"));
 
-    cmd.env(
-        "CARGO_TARGET_DIR",
-        format!(
-            "{}/test-crates/targets/{unique_name}",
-            env!("CARGO_MANIFEST_DIR")
-        ),
-    );
+    let target_dir = target_dir(unique_name);
+    cmd.env("CARGO_TARGET_DIR", target_dir);
 
     // Building with `--no-build-isolation` means that `maturin` needs to be on PATH _and_
     // importable
@@ -91,3 +93,19 @@ fn insert_path(env_var: &str, new_path: &Path) -> String {
         .into_string()
         .expect("PATH is not valid utf8")
 }
+
+/// Whether cargo built the shared library for the specified cargo profile in the test target
+/// directory.
+pub fn target_has_profile(unique_name: &str, profile: &str) -> bool {
+    let shared_library = if cfg!(windows) {
+        "pyo3_pure.dll"
+    } else if cfg!(target_os = "macos") {
+        "libpyo3_pure.dylib"
+    } else {
+        "libpyo3_pure.so"
+    };
+    PathBuf::from(target_dir(unique_name))
+        .join(profile)
+        .join(shared_library)
+        .is_file()
+}
diff --git a/tests/run.rs b/tests/run.rs
index b5873804f..c678bf88a 100644
--- a/tests/run.rs
+++ b/tests/run.rs
@@ -1,5 +1,6 @@
 //! To speed up the tests, they are tests all collected in a single module
 
+use common::pep517::{target_has_profile, test_pep517};
 use common::{
     TestInstallBackend, develop, errors, handle_result, integration, other,
     test_python_implementation,
@@ -14,8 +15,6 @@ use std::time::Duration;
 use time::macros::datetime;
 use which::which;
 
-use crate::common::{find_subslice, pep517};
-
 mod common;
 
 #[test]
@@ -1004,32 +1003,28 @@ fn sdist_source_date_epoch() {
 
 #[test]
 fn pep517_default_profile() {
-    let output = handle_result(pep517::test_pep517(
+    let unique_name = "pep517-pyo3-pure";
+    handle_result(test_pep517(
         "test-crates/pyo3-pure",
-        "pep517-pyo3-pure",
+        unique_name,
         false,
         false,
     ));
 
-    assert!(
-        find_subslice(&output.stderr, b"`release` profile [optimized]").is_some(),
-        "Output was: {}",
-        std::str::from_utf8(&output.stderr).unwrap()
-    );
+    assert!(target_has_profile(unique_name, "release"));
+    assert!(!target_has_profile(unique_name, "debug"));
 }
 
 #[test]
 fn pep517_editable_profile() {
-    let output = handle_result(pep517::test_pep517(
+    let unique_name = "pep517-pyo3-pure-editable";
+    handle_result(test_pep517(
         "test-crates/pyo3-pure",
-        "pep517-pyo3-pure-editable",
+        unique_name,
         false,
         true,
     ));
 
-    assert!(
-        find_subslice(&output.stderr, b"`dev` profile [unoptimized + debuginfo]").is_some(),
-        "Output was: {}",
-        std::str::from_utf8(&output.stderr).unwrap()
-    );
+    assert!(!target_has_profile(unique_name, "release"));
+    assert!(target_has_profile(unique_name, "debug"));
 }