diff --git a/nac3core/src/inference.rs b/nac3core/src/inference.rs
index a0820f5c..1eb351e6 100644
--- a/nac3core/src/inference.rs
+++ b/nac3core/src/inference.rs
@@ -197,3 +197,395 @@ pub fn resolve_call(
 ) -> Result<Option<Rc<Type>>, String> {
     resolve_call_rec(ctx, &None, obj, func, args)
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::primitives::*;
+
+    #[test]
+    fn test_simple_generic() {
+        let mut ctx = basic_ctx();
+
+        assert_eq!(
+            resolve_call(&ctx, None, "int32", &[PrimitiveType(FLOAT_TYPE).into()]),
+            Ok(Some(PrimitiveType(INT32_TYPE).into()))
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "int32", &[PrimitiveType(INT32_TYPE).into()],),
+            Ok(Some(PrimitiveType(INT32_TYPE).into()))
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "float", &[PrimitiveType(INT32_TYPE).into()]),
+            Ok(Some(PrimitiveType(FLOAT_TYPE).into()))
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "float", &[PrimitiveType(BOOL_TYPE).into()]),
+            Err("different domain".to_string())
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "float", &[]),
+            Err("incorrect parameter number".to_string())
+        );
+
+        let v1 = ctx.add_variable(VarDef {
+            name: "V1",
+            bound: vec![
+                PrimitiveType(INT32_TYPE).into(),
+                PrimitiveType(FLOAT_TYPE).into(),
+            ],
+        });
+
+        assert_eq!(
+            resolve_call(&ctx, None, "float", &[TypeVariable(v1).into()]),
+            Ok(Some(PrimitiveType(FLOAT_TYPE).into()))
+        );
+
+        let v2 = ctx.add_variable(VarDef {
+            name: "V2",
+            bound: vec![
+                PrimitiveType(BOOL_TYPE).into(),
+                PrimitiveType(INT32_TYPE).into(),
+                PrimitiveType(FLOAT_TYPE).into(),
+            ],
+        });
+
+        assert_eq!(
+            resolve_call(&ctx, None, "float", &[TypeVariable(v2).into()]),
+            Err("different domain".to_string())
+        );
+    }
+
+    #[test]
+    fn test_methods() {
+        let mut ctx = basic_ctx();
+
+        let v0 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V0",
+            bound: vec![],
+        })));
+        let v1 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V1",
+            bound: vec![
+                PrimitiveType(INT32_TYPE).into(),
+                PrimitiveType(FLOAT_TYPE).into(),
+            ],
+        })));
+        let v2 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V2",
+            bound: vec![
+                PrimitiveType(INT32_TYPE).into(),
+                PrimitiveType(FLOAT_TYPE).into(),
+            ],
+        })));
+        let v3 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V3",
+            bound: vec![
+                PrimitiveType(BOOL_TYPE).into(),
+                PrimitiveType(INT32_TYPE).into(),
+                PrimitiveType(FLOAT_TYPE).into(),
+            ],
+        })));
+
+        let int32 = Rc::new(PrimitiveType(INT32_TYPE));
+        let int64 = Rc::new(PrimitiveType(INT64_TYPE));
+
+        // simple cases
+        assert_eq!(
+            resolve_call(&ctx, Some(int32.clone()), "__add__", &[int32.clone()]),
+            Ok(Some(int32.clone()))
+        );
+
+        assert_ne!(
+            resolve_call(&ctx, Some(int32.clone()), "__add__", &[int32.clone()]),
+            Ok(Some(int64.clone()))
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, Some(int32.clone()), "__add__", &[int64.clone()]),
+            Err("not equal".to_string())
+        );
+
+        // with type variables
+        assert_eq!(
+            resolve_call(&ctx, Some(v1.clone()), "__add__", &[v1.clone()]),
+            Ok(Some(v1.clone()))
+        );
+        assert_eq!(
+            resolve_call(&ctx, Some(v0.clone()), "__add__", &[v2.clone()]),
+            Err("unbounded type var".to_string())
+        );
+        assert_eq!(
+            resolve_call(&ctx, Some(v1.clone()), "__add__", &[v0.clone()]),
+            Err("different domain".to_string())
+        );
+        assert_eq!(
+            resolve_call(&ctx, Some(v1.clone()), "__add__", &[v2.clone()]),
+            Err("different domain".to_string())
+        );
+        assert_eq!(
+            resolve_call(&ctx, Some(v1.clone()), "__add__", &[v3.clone()]),
+            Err("different domain".to_string())
+        );
+        assert_eq!(
+            resolve_call(&ctx, Some(v3.clone()), "__add__", &[v1.clone()]),
+            Err("no such function".to_string())
+        );
+        assert_eq!(
+            resolve_call(&ctx, Some(v3.clone()), "__add__", &[v3.clone()]),
+            Err("no such function".to_string())
+        );
+    }
+
+    #[test]
+    fn test_multi_generic() {
+        let mut ctx = basic_ctx();
+        let v0 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V0",
+            bound: vec![],
+        })));
+        let v1 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V1",
+            bound: vec![],
+        })));
+        let v2 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V2",
+            bound: vec![],
+        })));
+        let v3 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V3",
+            bound: vec![],
+        })));
+
+        ctx.add_fn(
+            "foo",
+            FnDef {
+                args: vec![v0.clone(), v0.clone(), v1.clone()],
+                result: Some(v0.clone()),
+            },
+        );
+
+        ctx.add_fn(
+            "foo1",
+            FnDef {
+                args: vec![
+                    ParametricType(TUPLE_TYPE, vec![v0.clone(), v0.clone(), v1.clone()]).into(),
+                ],
+                result: Some(v0.clone()),
+            },
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[v2.clone(), v2.clone(), v2.clone()]),
+            Ok(Some(v2.clone()))
+        );
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[v2.clone(), v2.clone(), v3.clone()]),
+            Ok(Some(v2.clone()))
+        );
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[v2.clone(), v3.clone(), v3.clone()]),
+            Err("different variables".to_string())
+        );
+
+        assert_eq!(
+            resolve_call(
+                &ctx,
+                None,
+                "foo1",
+                &[ParametricType(TUPLE_TYPE, vec![v2.clone(), v2.clone(), v2.clone()]).into()]
+            ),
+            Ok(Some(v2.clone()))
+        );
+        assert_eq!(
+            resolve_call(
+                &ctx,
+                None,
+                "foo1",
+                &[ParametricType(TUPLE_TYPE, vec![v2.clone(), v2.clone(), v3.clone()]).into()]
+            ),
+            Ok(Some(v2.clone()))
+        );
+        assert_eq!(
+            resolve_call(
+                &ctx,
+                None,
+                "foo1",
+                &[ParametricType(TUPLE_TYPE, vec![v2.clone(), v3.clone(), v3.clone()]).into()]
+            ),
+            Err("different variables".to_string())
+        );
+    }
+
+    #[test]
+    fn test_class_generics() {
+        let mut ctx = basic_ctx();
+
+        let list = ctx.get_parametric_mut(LIST_TYPE);
+        let t = Rc::new(TypeVariable(list.params[0]));
+        list.base.methods.insert(
+            "head",
+            FnDef {
+                args: vec![],
+                result: Some(t.clone()),
+            },
+        );
+        list.base.methods.insert(
+            "append",
+            FnDef {
+                args: vec![t.clone()],
+                result: None,
+            },
+        );
+
+        let v0 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V0",
+            bound: vec![],
+        })));
+        let v1 = Rc::new(TypeVariable(ctx.add_variable(VarDef {
+            name: "V1",
+            bound: vec![],
+        })));
+
+        assert_eq!(
+            resolve_call(
+                &ctx,
+                Some(ParametricType(LIST_TYPE, vec![v0.clone()]).into()),
+                "head",
+                &[]
+            ),
+            Ok(Some(v0.clone()))
+        );
+        assert_eq!(
+            resolve_call(
+                &ctx,
+                Some(ParametricType(LIST_TYPE, vec![v0.clone()]).into()),
+                "append",
+                &[v0.clone()]
+            ),
+            Ok(None)
+        );
+        assert_eq!(
+            resolve_call(
+                &ctx,
+                Some(ParametricType(LIST_TYPE, vec![v0.clone()]).into()),
+                "append",
+                &[v1.clone()]
+            ),
+            Err("different variables".to_string())
+        );
+    }
+
+    #[test]
+    fn test_virtual_class() {
+        let mut ctx = basic_ctx();
+
+        let foo = ctx.add_class(ClassDef {
+            base: TypeDef {
+                name: "Foo",
+                methods: HashMap::new(),
+                fields: HashMap::new(),
+            },
+            parents: vec![],
+        });
+
+        let foo1 = ctx.add_class(ClassDef {
+            base: TypeDef {
+                name: "Foo1",
+                methods: HashMap::new(),
+                fields: HashMap::new(),
+            },
+            parents: vec![foo],
+        });
+
+        let foo2 = ctx.add_class(ClassDef {
+            base: TypeDef {
+                name: "Foo2",
+                methods: HashMap::new(),
+                fields: HashMap::new(),
+            },
+            parents: vec![foo1],
+        });
+
+        let bar = ctx.add_class(ClassDef {
+            base: TypeDef {
+                name: "bar",
+                methods: HashMap::new(),
+                fields: HashMap::new(),
+            },
+            parents: vec![],
+        });
+
+        ctx.add_fn(
+            "foo",
+            FnDef {
+                args: vec![VirtualClassType(foo).into()],
+                result: None,
+            },
+        );
+        ctx.add_fn(
+            "foo1",
+            FnDef {
+                args: vec![VirtualClassType(foo1).into()],
+                result: None,
+            },
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[ClassType(foo).into()]),
+            Ok(None)
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[ClassType(foo1).into()]),
+            Ok(None)
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[ClassType(foo2).into()]),
+            Ok(None)
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[ClassType(bar).into()]),
+            Err("not subtype".to_string())
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "foo1", &[ClassType(foo1).into()]),
+            Ok(None)
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "foo1", &[ClassType(foo2).into()]),
+            Ok(None)
+        );
+
+        assert_eq!(
+            resolve_call(&ctx, None, "foo1", &[ClassType(foo).into()]),
+            Err("not subtype".to_string())
+        );
+
+        // virtual class substitution
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[VirtualClassType(foo).into()]),
+            Ok(None)
+        );
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[VirtualClassType(foo1).into()]),
+            Ok(None)
+        );
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[VirtualClassType(foo2).into()]),
+            Ok(None)
+        );
+        assert_eq!(
+            resolve_call(&ctx, None, "foo", &[VirtualClassType(bar).into()]),
+            Err("not subtype".to_string())
+        );
+    }
+}