diff --git a/Cargo.lock b/Cargo.lock
index 4cdd0de23..5bc02ac38 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -19,18 +19,48 @@ dependencies = [
  "version_check",
 ]
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "allocator-api2"
 version = "0.2.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0942ffc6dcaadf03badf6e6a2d0228460359d5e34b57ccdc720b7382dfbd5ec5"
 
+[[package]]
+name = "anstyle"
+version = "1.0.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1bec1de6f59aedf83baf9ff929c98f2ad654b97c9510f4e70cf6f661d49fd5b1"
+
 [[package]]
 name = "arraydeque"
 version = "0.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7d902e3d592a523def97af8f317b08ce16b7ab854c1985a0c671e6f15cebc236"
 
+[[package]]
+name = "assert_fs"
+version = "1.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7efdb1fdb47602827a342857666feb372712cbc64b414172bd6b167a02927674"
+dependencies = [
+ "anstyle",
+ "doc-comment",
+ "globwalk",
+ "predicates",
+ "predicates-core",
+ "predicates-tree",
+ "tempfile",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.1.0"
@@ -52,6 +82,16 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "bstr"
+version = "1.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "40723b8fb387abc38f4f4a37c09073622e41dd12327033091ef8950659e6dc0c"
+dependencies = [
+ "memchr",
+ "serde",
+]
+
 [[package]]
 name = "byteorder"
 version = "1.5.0"
@@ -82,6 +122,31 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "crossbeam-deque"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "613f8cc01fe9cf1a3eb3d7f488fd2fa8388403e97039e2f73692932e291a770d"
+dependencies = [
+ "crossbeam-epoch",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+dependencies = [
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-utils"
+version = "0.8.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22ec99545bb0ed0ea7bb9b8e1e9122ea386ff8a48c0922e43f36d45ab09e0e80"
+
 [[package]]
 name = "crypto-common"
 version = "0.1.6"
@@ -96,17 +161,25 @@ dependencies = [
 name = "dekoder"
 version = "0.0.1"
 dependencies = [
+ "assert_fs",
  "float-cmp",
  "glob",
  "hashbrown",
  "lz4_flex",
  "ndarray",
  "ndarray-npy",
+ "predicates",
  "tar",
  "thiserror",
  "yaml-rust2",
 ]
 
+[[package]]
+name = "difflib"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6184e33543162437515c2e2b48714794e37845ec9851711914eec9d308f6ebe8"
+
 [[package]]
 name = "digest"
 version = "0.10.7"
@@ -117,6 +190,12 @@ dependencies = [
  "crypto-common",
 ]
 
+[[package]]
+name = "doc-comment"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fea41bba32d969b513997752735605054bc0dfa92b4c56bf1189f2e174be7a10"
+
 [[package]]
 name = "eko"
 version = "0.0.1"
@@ -153,6 +232,12 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "fastrand"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9fc0510504f03c51ada170672ac806f1f105a88aa97a5281117e1ddc3368e51a"
+
 [[package]]
 name = "filetime"
 version = "0.2.24"
@@ -200,6 +285,30 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d2fabcfbdc87f4758337ca535fb41a6d701b65693ce38287d856d1674551ec9b"
 
+[[package]]
+name = "globset"
+version = "0.4.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "57da3b9b5b85bd66f31093f8c408b90a74431672542466497dcbdfdc02034be1"
+dependencies = [
+ "aho-corasick",
+ "bstr",
+ "log",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "globwalk"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0bf760ebf69878d9fd8f110c89703d90ce35095324d1f1edcb595c63945ee757"
+dependencies = [
+ "bitflags",
+ "ignore",
+ "walkdir",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.14.0"
@@ -219,6 +328,22 @@ dependencies = [
  "hashbrown",
 ]
 
+[[package]]
+name = "ignore"
+version = "0.4.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b46810df39e66e925525d6e38ce1e7f6e1d208f72dc39757880fcb66e2c58af1"
+dependencies = [
+ "crossbeam-deque",
+ "globset",
+ "log",
+ "memchr",
+ "regex-automata",
+ "same-file",
+ "walkdir",
+ "winapi-util",
+]
+
 [[package]]
 name = "libc"
 version = "0.2.155"
@@ -242,6 +367,12 @@ version = "0.4.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "78b3ae25bc7c8c38cec158d1f2757ee79e9b3740fbc7ccf0e59e4b08d793fa89"
 
+[[package]]
+name = "log"
+version = "0.4.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a7a70ba024b9dc04c27ea2f0c0548feb474ec5c54bba33a7f72f873a39d07b24"
+
 [[package]]
 name = "lz4_flex"
 version = "0.9.5"
@@ -303,6 +434,12 @@ dependencies = [
  "zip",
 ]
 
+[[package]]
+name = "normalize-line-endings"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "61807f77802ff30975e01f4f071c8ba10c022052f98b3294119f3e615d13e5be"
+
 [[package]]
 name = "num"
 version = "0.4.1"
@@ -430,6 +567,36 @@ dependencies = [
  "sha2",
 ]
 
+[[package]]
+name = "predicates"
+version = "3.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7e9086cc7640c29a356d1a29fd134380bee9d8f79a17410aa76e7ad295f42c97"
+dependencies = [
+ "anstyle",
+ "difflib",
+ "float-cmp",
+ "normalize-line-endings",
+ "predicates-core",
+ "regex",
+]
+
+[[package]]
+name = "predicates-core"
+version = "1.0.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae8177bee8e75d6846599c6b9ff679ed51e882816914eec639944d7c9aa11931"
+
+[[package]]
+name = "predicates-tree"
+version = "1.0.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41b740d195ed3166cd147c8047ec98db0e22ec019eb8eeb76d343b795304fb13"
+dependencies = [
+ "predicates-core",
+ "termtree",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.86"
@@ -476,6 +643,35 @@ dependencies = [
  "bitflags",
 ]
 
+[[package]]
+name = "regex"
+version = "1.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4219d74c6b67a3654a9fbebc4b419e22126d13d2f3c4a07ee0cb61ff79a79619"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38caf58cc5ef2fed281f89292ef23f6365465ed9a41b7a7754eb4e26496c92df"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a66a03ae7c801facd77a29370b4faec201768915ac14a721ba36f20bc9c209b"
+
 [[package]]
 name = "rustix"
 version = "0.38.34"
@@ -489,6 +685,35 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
+[[package]]
+name = "same-file"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "93fc1dc3aaa9bfed95e02e6eadabb4baf7e3078b0bd1b4d7b6b0b68378900502"
+dependencies = [
+ "winapi-util",
+]
+
+[[package]]
+name = "serde"
+version = "1.0.208"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cff085d2cb684faa248efb494c39b68e522822ac0de72ccf08109abde717cfb2"
+dependencies = [
+ "serde_derive",
+]
+
+[[package]]
+name = "serde_derive"
+version = "1.0.208"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24008e81ff7613ed8e5ba0cfaf24e2c2f1e5b8a0495711e44fcd4882fca62bcf"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "sha2"
 version = "0.10.8"
@@ -528,6 +753,24 @@ dependencies = [
  "xattr",
 ]
 
+[[package]]
+name = "tempfile"
+version = "3.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85b77fafb263dd9d05cbeac119526425676db3784113aa9295c88498cbf8bff1"
+dependencies = [
+ "cfg-if",
+ "fastrand",
+ "rustix",
+ "windows-sys 0.52.0",
+]
+
+[[package]]
+name = "termtree"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3369f5ac52d5eb6ab48c6b4ffdc8efbcad6b89c765749064ba298f2c68a16a76"
+
 [[package]]
 name = "thiserror"
 version = "1.0.63"
@@ -582,6 +825,25 @@ version = "0.9.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
 
+[[package]]
+name = "walkdir"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29790946404f91d9c5d06f9874efddea1dc06c5efe94541a7d6863108e3a5e4b"
+dependencies = [
+ "same-file",
+ "winapi-util",
+]
+
+[[package]]
+name = "winapi-util"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf221c93e13a30d793f7645a0e7762c55d169dbb0a49671918a2319d289b10bb"
+dependencies = [
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.52.0"
diff --git a/crates/dekoder/Cargo.toml b/crates/dekoder/Cargo.toml
index 5f3555e93..605e79473 100644
--- a/crates/dekoder/Cargo.toml
+++ b/crates/dekoder/Cargo.toml
@@ -25,3 +25,7 @@ lz4_flex = "0.9.2"
 ndarray = "0.15.4"
 ndarray-npy = "0.8.1"
 thiserror = "1.0.63"
+
+[dev-dependencies]
+assert_fs = "1.1.2"
+predicates = "3.1.2"
diff --git a/crates/dekoder/tests/test_load.rs b/crates/dekoder/tests/test_load.rs
index bb999ddb9..560ef9ca9 100644
--- a/crates/dekoder/tests/test_load.rs
+++ b/crates/dekoder/tests/test_load.rs
@@ -1,55 +1,34 @@
-use dekoder::{EvolutionPoint, Operator, EKO};
-use std::fs::{remove_dir_all, remove_file};
+use assert_fs::prelude::*;
+use predicates::prelude::*;
 use std::path::PathBuf;
 
-#[test]
-fn save_as_other() {
+use dekoder::{EvolutionPoint, Operator, EKO};
+
+/// Get v0.15 test object
+fn v015tar() -> PathBuf {
     let base: PathBuf = [env!("CARGO_MANIFEST_DIR"), "tests"].iter().collect();
     let src = base.join("data").join("v0.15.tar");
-    assert!(src.try_exists().is_ok_and(|x| x));
-    let dst = base.join("target").join("v0.15a");
-    // get rid of previous runs if needed
-    let dst_exists = dst.try_exists().is_ok_and(|x| x);
-    if dst_exists {
-        remove_dir_all(dst.to_owned()).unwrap();
-    }
+    assert!(predicate::path::exists().eval(&src));
+    src
+}
+
+#[test]
+fn save_as_other() {
+    let src = v015tar();
+    let dst = assert_fs::TempDir::new().unwrap();
     // open
     let mut eko = EKO::edit(src.to_owned(), dst.to_owned()).unwrap();
-    let dst_exists = dst.try_exists().is_ok_and(|x| x);
-    assert!(dst_exists);
-    // set a different output
-    let tarb = base.join("target").join("v0.15b.tar");
-    let tarb_exists = tarb.try_exists().is_ok_and(|x| x);
-    if tarb_exists {
-        remove_file(tarb.to_owned()).unwrap();
-    }
+    // write to somewhere else
+    let tarb = assert_fs::NamedTempFile::new("v0.15b.tar").unwrap();
     eko.set_tar_path(tarb.to_owned());
-    // close
     eko.close(true).unwrap();
-    let tarb_exists = tarb.try_exists().is_ok_and(|x| x);
-    assert!(tarb_exists);
-    let dst_exists = dst.try_exists().is_ok_and(|x| x);
-    assert!(!dst_exists);
-    // clean up
-    if tarb_exists {
-        remove_file(tarb.to_owned()).unwrap();
-    }
-    if dst_exists {
-        remove_dir_all(dst.to_str().unwrap()).unwrap();
-    }
+    tarb.assert(predicate::path::exists());
 }
 
 #[test]
 fn has_operator() {
-    let base: PathBuf = [env!("CARGO_MANIFEST_DIR"), "tests"].iter().collect();
-    let src = base.join("data").join("v0.15.tar");
-    assert!(src.try_exists().is_ok_and(|x| x));
-    let dst = base.join("target").join("v0.15b");
-    // get rid of previous runs if needed
-    let dst_exists = dst.try_exists().is_ok_and(|x| x);
-    if dst_exists {
-        remove_dir_all(dst.to_owned()).unwrap();
-    }
+    let src = v015tar();
+    let dst = assert_fs::TempDir::new().unwrap();
     // open
     let eko = EKO::read(src.to_owned(), dst.to_owned()).unwrap();
     // check there is only one:
@@ -67,17 +46,11 @@ fn has_operator() {
 
 #[test]
 fn load_operator() {
-    let base: PathBuf = [env!("CARGO_MANIFEST_DIR"), "tests"].iter().collect();
-    let src = base.join("data").join("v0.15.tar");
-    assert!(src.try_exists().is_ok_and(|x| x));
-    let dst = base.join("target").join("v0.15c");
-    // get rid of previous runs if needed
-    let dst_exists = dst.try_exists().is_ok_and(|x| x);
-    if dst_exists {
-        remove_dir_all(dst.to_owned()).unwrap();
-    }
+    let src = v015tar();
+    let dst = assert_fs::TempDir::new().unwrap();
     // open
     let mut eko = EKO::read(src.to_owned(), dst.to_owned()).unwrap();
+    // load
     let ep = EvolutionPoint {
         scale: 10000.,
         nf: 4,