diff --git a/Cargo.lock b/Cargo.lock
index 68d6fd3..4b605bd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -35,6 +35,18 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
+[[package]]
+name = "console"
+version = "0.15.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0e1f83fc076bd6dd27517eacdf25fef6c4dfe5f1d7448bafaaf3a26f13b5e4eb"
+dependencies = [
+ "encode_unicode",
+ "lazy_static",
+ "libc",
+ "windows-sys 0.52.0",
+]
+
 [[package]]
 name = "dylo"
 version = "1.0.1"
@@ -45,7 +57,9 @@ version = "1.0.3"
 dependencies = [
  "camino",
  "fs-err",
+ "insta",
  "pico-args",
+ "prettyplease",
  "proc-macro2",
  "quote",
  "rustfmt-wrapper",
@@ -63,6 +77,12 @@ dependencies = [
  "rubicon",
 ]
 
+[[package]]
+name = "encode_unicode"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a357d28ed41a50f9c765dbfe56cbc04a64e53e5fc58ba79fbc34c10ef3df831f"
+
 [[package]]
 name = "equivalent"
 version = "1.0.1"
@@ -119,6 +139,18 @@ dependencies = [
  "hashbrown",
 ]
 
+[[package]]
+name = "insta"
+version = "1.41.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7e9ffc4d4892617c50a928c52b2961cb5174b6fc6ebf252b2fac9d21955c48b8"
+dependencies = [
+ "console",
+ "lazy_static",
+ "linked-hash-map",
+ "similar",
+]
+
 [[package]]
 name = "lazy_static"
 version = "1.5.0"
@@ -131,6 +163,12 @@ version = "0.2.167"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "09d6582e104315a817dff97f75133544b2e094ee22447d2acf4a74e189ba06fc"
 
+[[package]]
+name = "linked-hash-map"
+version = "0.5.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0717cef1bc8b636c6e1c1bbdefc09e6322da8a9321966e8928ef80d20f7f770f"
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.4.14"
@@ -189,6 +227,16 @@ version = "0.2.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "915a1e146535de9163f3987b8944ed8cf49a18bb0056bcebcdcece385cece4ff"
 
+[[package]]
+name = "prettyplease"
+version = "0.2.25"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "64d1ec885c64d0457d564db4ec299b2dae3f9c02808b8ad9c3a089c591b18033"
+dependencies = [
+ "proc-macro2",
+ "syn",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.92"
@@ -335,6 +383,12 @@ dependencies = [
  "lazy_static",
 ]
 
+[[package]]
+name = "similar"
+version = "2.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1de1d4f81173b03af4c0cbed3c898f6bff5b870e4a7f5d6f4057d62a7a4b686e"
+
 [[package]]
 name = "smallvec"
 version = "1.13.2"
diff --git a/Justfile b/Justfile
index f95548b..992bff0 100644
--- a/Justfile
+++ b/Justfile
@@ -1,3 +1,3 @@
 
 test:
-  cargo build --release -p dylo-runtime
+  cargo t
diff --git a/dylo-cli/Cargo.toml b/dylo-cli/Cargo.toml
index b97a58c..f138658 100644
--- a/dylo-cli/Cargo.toml
+++ b/dylo-cli/Cargo.toml
@@ -27,3 +27,7 @@ toml_edit = "0.22.22"
 camino = "1.1.9"
 pico-args = "0.5.0"
 tracing = "0.1.41"
+prettyplease = "0.2.25"
+
+[dev-dependencies]
+insta = "1.41.1"
diff --git a/dylo-cli/src/main.rs b/dylo-cli/src/main.rs
index b0a4b4d..5fb9cb3 100644
--- a/dylo-cli/src/main.rs
+++ b/dylo-cli/src/main.rs
@@ -490,28 +490,29 @@ fn process_mod(mod_info: ModInfo, force: bool) -> std::io::Result<()> {
     Ok(())
 }
 
-fn item_attributes(item: &Item) -> Option<&Vec<Attribute>> {
+fn item_attributes(item: &mut Item) -> Option<&mut Vec<Attribute>> {
     match item {
-        Item::Const(item) => Some(&item.attrs),
-        Item::Enum(item) => Some(&item.attrs),
-        Item::ExternCrate(item) => Some(&item.attrs),
-        Item::Fn(item) => Some(&item.attrs),
-        Item::ForeignMod(item) => Some(&item.attrs),
-        Item::Impl(item) => Some(&item.attrs),
-        Item::Macro(item) => Some(&item.attrs),
-        Item::Mod(item) => Some(&item.attrs),
-        Item::Static(item) => Some(&item.attrs),
-        Item::Struct(item) => Some(&item.attrs),
-        Item::Trait(item) => Some(&item.attrs),
-        Item::TraitAlias(item) => Some(&item.attrs),
-        Item::Type(item) => Some(&item.attrs),
-        Item::Union(item) => Some(&item.attrs),
-        Item::Use(item) => Some(&item.attrs),
+        Item::Const(item) => Some(&mut item.attrs),
+        Item::Enum(item) => Some(&mut item.attrs),
+        Item::ExternCrate(item) => Some(&mut item.attrs),
+        Item::Fn(item) => Some(&mut item.attrs),
+        Item::ForeignMod(item) => Some(&mut item.attrs),
+        Item::Impl(item) => Some(&mut item.attrs),
+        Item::Macro(item) => Some(&mut item.attrs),
+        Item::Mod(item) => Some(&mut item.attrs),
+        Item::Static(item) => Some(&mut item.attrs),
+        Item::Struct(item) => Some(&mut item.attrs),
+        Item::Trait(item) => Some(&mut item.attrs),
+        Item::TraitAlias(item) => Some(&mut item.attrs),
+        Item::Type(item) => Some(&mut item.attrs),
+        Item::Union(item) => Some(&mut item.attrs),
+        Item::Use(item) => Some(&mut item.attrs),
         Item::Verbatim(_) => None,
         _ => None,
     }
 }
 
+// recognizes `#[cfg(feature = "impl"]`
 fn is_cfg_feature_impl(attr: &Attribute) -> bool {
     if !attr.path().is_ident("cfg") {
         return false;
@@ -530,6 +531,32 @@ fn is_cfg_feature_impl(attr: &Attribute) -> bool {
     has_feature_impl
 }
 
+// recognizes `#[cfg(not(feature = "impl"))]`
+fn is_cfg_not_feature_impl(attr: &Attribute) -> bool {
+    if !attr.path().is_ident("cfg") {
+        return false;
+    }
+
+    let mut has_not = false;
+    let mut has_feature_impl = false;
+    let _ = attr.parse_nested_meta(|meta| {
+        if meta.path.is_ident("not") {
+            let _ = meta.parse_nested_meta(|meta| {
+                if meta.path.is_ident("feature") {
+                    let content = meta.input.to_string();
+                    if content == "= \"impl\"" {
+                        has_feature_impl = true;
+                    }
+                }
+                Ok(())
+            });
+            has_not = true;
+        }
+        Ok(())
+    });
+    has_not && has_feature_impl
+}
+
 fn is_cfg_test(attr: &Attribute) -> bool {
     if !attr.path().is_ident("cfg") {
         return false;
@@ -545,7 +572,7 @@ fn is_cfg_test(attr: &Attribute) -> bool {
     has_test
 }
 
-fn should_remove_item(item: &Item) -> bool {
+fn should_remove_item(item: &mut Item) -> bool {
     if let Some(attrs) = item_attributes(item) {
         for attr in attrs {
             if is_cfg_feature_impl(attr) || is_cfg_test(attr) {
@@ -580,7 +607,7 @@ impl InterfaceType {
     }
 }
 
-fn transform_ast(items: &mut Vec<Item>, added_items: &mut Vec<Item>) {
+pub(crate) fn transform_ast(items: &mut Vec<Item>, added_items: &mut Vec<Item>) {
     items.retain_mut(|item| {
         let mut keep = true;
 
@@ -627,7 +654,13 @@ fn transform_ast(items: &mut Vec<Item>, added_items: &mut Vec<Item>) {
 
         if should_remove_item(item) {
             keep = false
+        } else {
+            // remove any cfg(not(feature = "impl")) attributes
+            if let Some(attrs) = item_attributes(item) {
+                attrs.retain(|attr| !is_cfg_not_feature_impl(attr));
+            }
         }
+
         keep
     });
 }
@@ -817,3 +850,6 @@ fn main() -> std::io::Result<()> {
 
     Ok(())
 }
+
+#[cfg(test)]
+mod tests;
diff --git a/dylo-cli/src/snapshots/dylo__tests__snapshot_simple_module.snap b/dylo-cli/src/snapshots/dylo__tests__snapshot_simple_module.snap
new file mode 100644
index 0000000..f6d49b3
--- /dev/null
+++ b/dylo-cli/src/snapshots/dylo__tests__snapshot_simple_module.snap
@@ -0,0 +1,18 @@
+---
+source: dylo-cli/src/tests.rs
+expression: output
+snapshot_kind: text
+---
+fn not_impl_only() {}
+enum NotImplEnum {
+    Variant1,
+    Variant2,
+}
+impl NotImplEnum {
+    fn variant1(&self) -> u32 {
+        23
+    }
+}
+pub trait Mod: Send + Sync + 'static {
+    fn foo(&self) -> u32;
+}
diff --git a/dylo-cli/src/testdata/simple-module.rs b/dylo-cli/src/testdata/simple-module.rs
new file mode 100644
index 0000000..1e3a333
--- /dev/null
+++ b/dylo-cli/src/testdata/simple-module.rs
@@ -0,0 +1,43 @@
+#[cfg(feature = "impl")]
+use impl_only;
+
+#[cfg(feature = "impl")]
+fn impl_only() {}
+
+#[cfg(not(feature = "impl"))]
+fn not_impl_only() {}
+
+#[cfg(feature = "impl")]
+#[derive(Default)]
+struct ModImpl;
+
+#[dylo::export]
+impl Mod for ModImpl {
+    fn foo(&self) -> u32 {
+        42
+    }
+}
+
+#[cfg(feature = "impl")]
+enum ImplEnum {
+    Variant1,
+    Variant2,
+}
+
+#[cfg(feature = "impl")]
+impl ImplEnum {
+    fn variant1(&self) -> u32 {
+        23
+    }
+}
+
+enum NotImplEnum {
+    Variant1,
+    Variant2,
+}
+
+impl NotImplEnum {
+    fn variant1(&self) -> u32 {
+        23
+    }
+}
diff --git a/dylo-cli/src/tests.rs b/dylo-cli/src/tests.rs
new file mode 100644
index 0000000..004cd91
--- /dev/null
+++ b/dylo-cli/src/tests.rs
@@ -0,0 +1,15 @@
+use super::*;
+
+#[test]
+fn snapshot_simple_module() {
+    let input_rs = include_str!("testdata/simple-module.rs");
+    let mut file = syn::parse_file(input_rs).unwrap();
+
+    let mut added_items = Vec::new();
+    transform_ast(&mut file.items, &mut added_items);
+
+    file.items.extend(added_items);
+
+    let output = prettyplease::unparse(&file);
+    insta::assert_snapshot!(output);
+}
diff --git a/dylo-runtime/README.md b/dylo-runtime/README.md
index 568933b..4dee127 100644
--- a/dylo-runtime/README.md
+++ b/dylo-runtime/README.md
@@ -28,7 +28,7 @@ should be pre-built, and put in the right place, next to the executable.
 
 That is, if your Cargo workspace looks like this:
 
-```
+```text,ignore
 workspace/
   Cargo.toml
   mods/
@@ -43,7 +43,7 @@ workspace/
 
 Then `dylo-runtime` expects a file hierarchy like this:
 
-```
+```text,ignore
 workspace/
   target/
     debug/
diff --git a/test-workspace/Cargo.toml b/test-workspace/Cargo.toml
deleted file mode 100644
index 817396b..0000000
--- a/test-workspace/Cargo.toml
+++ /dev/null
@@ -1,22 +0,0 @@
-[workspace]
-members = [
-    "app",
-    "mods/*",
-]
-exclude = [
-    "test-workspace",
-]
-resolver = "2"
-
-[profile.dev]
-debug = 1
-split-debuginfo = "unpacked"
-incremental = true
-
-[profile.dev.package."*"]
-opt-level = 2
-
-[profile.release]
-debug = 1
-lto = "off"
-split-debuginfo = "unpacked"
diff --git a/test-workspace/app/Cargo.toml b/test-workspace/app/Cargo.toml
deleted file mode 100644
index 211d3b2..0000000
--- a/test-workspace/app/Cargo.toml
+++ /dev/null
@@ -1,6 +0,0 @@
-[package]
-name = "app"
-version = "0.1.0"
-edition = "2021"
-
-[dependencies]
diff --git a/test-workspace/app/src/main.rs b/test-workspace/app/src/main.rs
deleted file mode 100644
index e7a11a9..0000000
--- a/test-workspace/app/src/main.rs
+++ /dev/null
@@ -1,3 +0,0 @@
-fn main() {
-    println!("Hello, world!");
-}
diff --git a/test-workspace/mods/mod-clap/Cargo.toml b/test-workspace/mods/mod-clap/Cargo.toml
deleted file mode 100644
index 17bb7bf..0000000
--- a/test-workspace/mods/mod-clap/Cargo.toml
+++ /dev/null
@@ -1,6 +0,0 @@
-[package]
-name = "mod-clap"
-version = "0.1.0"
-edition = "2021"
-
-[dependencies]
diff --git a/test-workspace/mods/mod-clap/src/lib.rs b/test-workspace/mods/mod-clap/src/lib.rs
deleted file mode 100644
index b93cf3f..0000000
--- a/test-workspace/mods/mod-clap/src/lib.rs
+++ /dev/null
@@ -1,14 +0,0 @@
-pub fn add(left: u64, right: u64) -> u64 {
-    left + right
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
-    }
-}