diff --git a/hugr-core/src/hugr/monomorphize.rs b/hugr-core/src/hugr/monomorphize.rs
index 9c2d6e56e..8a83850d4 100644
--- a/hugr-core/src/hugr/monomorphize.rs
+++ b/hugr-core/src/hugr/monomorphize.rs
@@ -209,17 +209,19 @@ mod test {
 
     use crate::builder::test::simple_dfg_hugr;
     use crate::builder::{
-        BuildHandle, Container, Dataflow, DataflowSubContainer, HugrBuilder, ModuleBuilder,
+        BuildHandle, Container, Dataflow, DataflowHugr, DataflowSubContainer, FunctionBuilder,
+        HugrBuilder, ModuleBuilder,
     };
-    use crate::extension::prelude::{UnpackTuple, USIZE_T};
-    use crate::extension::{EMPTY_REG, PRELUDE_REGISTRY};
-    use crate::hugr::monomorphize::remove_polyfuncs;
+    use crate::extension::prelude::{ConstUsize, UnpackTuple, USIZE_T};
+    use crate::extension::{ExtensionRegistry, EMPTY_REG, PRELUDE, PRELUDE_REGISTRY};
+    use crate::hugr::monomorphize::mangle_inner_func;
     use crate::ops::handle::FuncID;
     use crate::ops::Tag;
+    use crate::std_extensions::arithmetic::int_types::{self, INT_TYPES};
     use crate::types::{PolyFuncType, Signature, Type, TypeBound};
-    use crate::{Hugr, HugrView};
+    use crate::{type_row, Hugr, HugrView};
 
-    use super::{mangle_name, monomorphize};
+    use super::{mangle_name, monomorphize, remove_polyfuncs};
 
     #[rstest]
     fn test_null(simple_dfg_hugr: Hugr) {
@@ -358,8 +360,100 @@ mod test {
     }
 
     #[test]
-    fn test_flattening() {}
+    fn test_flattening() {
+        //polyf1 contains polyf2 contains monof -> pf1<a> and pf1<b> share pf2's and they share monof
+
+        let reg = ExtensionRegistry::try_new([int_types::EXTENSION.to_owned(), PRELUDE.to_owned()])
+            .unwrap();
+        let tv0 = || Type::new_var_use(0, TypeBound::Any);
+        let ity = || INT_TYPES[3].clone();
+
+        let mut outer = FunctionBuilder::new("mainish", Signature::new(ity(), USIZE_T)).unwrap();
+        let sig = PolyFuncType::new(
+            [TypeBound::Any.into()],
+            Signature::new(tv0(), vec![tv0(), USIZE_T, USIZE_T]),
+        );
+        let mut pf1 = outer.define_function("pf1", sig).unwrap();
+
+        let sig = PolyFuncType::new(
+            [TypeBound::Any.into()],
+            Signature::new(tv0(), vec![tv0(), USIZE_T]),
+        );
+        let mut pf2 = pf1.define_function("pf2", sig).unwrap();
+
+        let mono_func = {
+            let mut mono_b = pf2
+                .define_function("get_usz", Signature::new(type_row![], USIZE_T))
+                .unwrap();
+            let cst0 = mono_b.add_load_value(ConstUsize::new(1));
+            mono_b.finish_with_outputs([cst0]).unwrap()
+        };
+        let pf2 = {
+            let [inw] = pf2.input_wires_arr();
+
+            let [usz] = pf2
+                .call(mono_func.handle(), &[], [], &reg)
+                .unwrap()
+                .outputs_arr();
+
+            pf2.finish_with_outputs([inw, usz]).unwrap()
+        };
+        // pf1: Two calls to pf2, one depending on pf1's TypeArg, the other not
+        let [a, u] = pf1
+            .call(pf2.handle(), &[tv0().into()], pf1.input_wires(), &reg)
+            .unwrap()
+            .outputs_arr();
+        let [u1, u2] = pf1
+            .call(pf2.handle(), &[USIZE_T.into()], [u], &reg)
+            .unwrap()
+            .outputs_arr();
+        let pf1 = pf1.finish_with_outputs([a, u1, u2]).unwrap();
+        // Outer: two calls to pf1 with different TypeArgs
+        let [_, u, _] = outer
+            .call(pf1.handle(), &[ity().into()], outer.input_wires(), &reg)
+            .unwrap()
+            .outputs_arr();
+        let [_, u, _] = outer
+            .call(pf1.handle(), &[USIZE_T.into()], [u], &reg)
+            .unwrap()
+            .outputs_arr();
+        let hugr = outer.finish_hugr_with_outputs([u], &reg).unwrap();
+
+        let mono_hugr = monomorphize(hugr, &reg);
+        mono_hugr.validate(&reg).unwrap();
+        let funcs = mono_hugr
+            .nodes()
+            .filter_map(|n| mono_hugr.get_optype(n).as_func_defn().map(|fd| (n, fd)))
+            .collect_vec();
+        let pf2_name = mangle_inner_func("pf1", "pf2");
+        assert_eq!(
+            funcs.iter().map(|(_, fd)| &fd.name).sorted().collect_vec(),
+            vec![
+                &mangle_name("pf1", &[ity().into()]),
+                &mangle_name("pf1", &[USIZE_T.into()]),
+                &mangle_name(&pf2_name, &[ity().into()]), // from pf1<int>
+                &mangle_name(&pf2_name, &[USIZE_T.into()]), // from pf1<int> and (2*)pf1<USIZE_T>
+                &mangle_inner_func(&pf2_name, "get_usz"),
+                "mainish"
+            ]
+            .into_iter()
+            .sorted()
+            .collect_vec()
+        );
+        for (n, fd) in funcs {
+            assert!(fd.signature.params().is_empty());
+            assert!(mono_hugr.get_parent(n) == (fd.name != "mainish").then_some(mono_hugr.root()));
+        }
+    }
 
     #[test]
-    fn test_recursive() {}
+    fn test_not_flattened() {
+        //monof2 contains polyf3 (and instantiates) - not moved
+        //polyf4 contains polyf5 but not instantiated -> not moved
+    }
+
+    #[test]
+    fn test_recursive() {
+        // make map,
+    }
 }