diff --git a/Cargo.toml b/Cargo.toml
index 32de55d..1d85fa3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -25,6 +25,7 @@ regex = "1.11.1"
 semver = "1.0.23"
 serde = "1.0.215"
 serde_json = "1.0.133"
+tempfile = "3.14.0"
 thiserror = "2.0.4"
 ureq = { version = "2.12.1", features = ["json"] }
 url = "2.5.4"
@@ -33,6 +34,5 @@ zip = "2.2.1"
 [dev-dependencies]
 httpmock = "0.7.0"
 sha2 = "0.10.8"
-tempfile = "3.14.0"
 temp-env = "0.3.6"
 assertables = "9.4.0"
diff --git a/src/api/mod.rs b/src/api/mod.rs
index c2a8a83..7437afe 100644
--- a/src/api/mod.rs
+++ b/src/api/mod.rs
@@ -21,16 +21,6 @@ use std::{
 };
 use url::Url;
 
-/// Returns a string representation of the final segment of a Path.
-macro_rules! filename {
-    ( $x:expr ) => {{
-        $x.as_ref()
-            .file_name()
-            .unwrap_or(std::ffi::OsStr::new("UNKNOWN"))
-            .to_string_lossy()
-    }};
-}
-
 macro_rules! copy_err {
     ($x:expr, $y:expr, $z:expr) => {{
         Err(BuildError::File(
@@ -128,7 +118,7 @@ impl Api {
     /// Unpack download `file` in directory `into` and return the path to the
     /// unpacked directory.
     pub fn unpack<P: AsRef<Path>>(&self, into: P, file: P) -> Result<PathBuf, BuildError> {
-        info!(file:display = filename!(file); "unpacking");
+        info!(file:display = crate::filename!(&file); "unpacking");
         let zip = File::open(file)?;
         let mut archive = zip::ZipArchive::new(zip)?;
         archive.extract(&into)?;
diff --git a/src/lib.rs b/src/lib.rs
index 9f6fc24..0d0c638 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -125,5 +125,16 @@ impl<P: AsRef<Path>> Builder<P> {
     }
 }
 
+/// Returns a string representation of the final segment of a Path.
+macro_rules! filename {
+    ( $x:expr ) => {{
+        AsRef::<Path>::as_ref($x)
+            .file_name()
+            .unwrap_or(std::ffi::OsStr::new("UNKNOWN"))
+            .to_string_lossy()
+    }};
+}
+pub(crate) use filename;
+
 #[cfg(test)]
 mod tests;
diff --git a/src/pipeline/mod.rs b/src/pipeline/mod.rs
index 03d5835..29a21d2 100644
--- a/src/pipeline/mod.rs
+++ b/src/pipeline/mod.rs
@@ -1,7 +1,8 @@
 //! Build Pipeline interface definition.
 
 use crate::error::BuildError;
-use std::{path::Path, process::Command};
+use log::debug;
+use std::{io::Write, path::Path, process::Command};
 
 /// Defines the interface for build pipelines to configure, compile, and test
 /// PGXN distributions.
@@ -30,6 +31,20 @@ pub(crate) trait Pipeline<P: AsRef<Path>> {
     /// Returns the directory passed to [`new`].
     fn dir(&self) -> &P;
 
+    /// Attempts to write a temporary file to `dir` and returns `true` on
+    /// success and `false` on failure. The temporary file will be deleted.
+    fn is_writeable<D: AsRef<Path>>(&self, dir: D) -> bool {
+        debug!(dir:display = crate::filename!(&dir); "testing write access");
+        match tempfile::Builder::new()
+            .prefix("pgxn-")
+            .suffix(".test")
+            .tempfile_in(dir)
+        {
+            Ok(f) => write!(&f, "ok").is_ok(),
+            Err(_) => false,
+        }
+    }
+
     /// Run a command. Runs it with elevated privileges using `sudo` unless
     /// it's on Windows.
     fn run<S, I>(&self, cmd: &str, args: I, sudo: bool) -> Result<(), BuildError>
diff --git a/src/pipeline/tests.rs b/src/pipeline/tests.rs
index 5763362..408fb57 100644
--- a/src/pipeline/tests.rs
+++ b/src/pipeline/tests.rs
@@ -91,3 +91,14 @@ fn run() -> Result<(), BuildError> {
 
     Ok(())
 }
+
+#[test]
+fn is_writeable() -> Result<(), BuildError> {
+    let tmp = tempdir()?;
+
+    let pipe = TestPipeline::new(&tmp, false);
+    assert!(pipe.is_writeable(&tmp));
+    assert!(!pipe.is_writeable(tmp.path().join(" nonesuch")));
+
+    Ok(())
+}
diff --git a/src/tests.rs b/src/tests.rs
index 33f98e0..e5b8279 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -1,6 +1,6 @@
 use super::*;
 use serde_json::{json, Value};
-use std::{fs::File, io::Write, process::Command};
+use std::{fs::File, io::Write, path::PathBuf, process::Command};
 use tempfile::tempdir;
 
 fn release_meta(pipeline: &str) -> Value {
@@ -199,3 +199,11 @@ pub fn compile_mock(name: &str, dest: &str) {
         )
     }
 }
+
+#[test]
+fn filename() {
+    assert_eq!("string", filename!("string"));
+    assert_eq!("path", filename!(Path::new("path")));
+    let pb = PathBuf::from(r"C:\windows\system32.dll");
+    assert_eq!(r"C:\windows\system32.dll", filename!(&pb));
+}