Balance assertions (#133)

* Make metadata serializable

* Refactor tests to use steps

* Add a balance assertion test step

* Test balance deserialization

* Box the test steps

* Permit size difference in step output

crates/format/src/input.rs

@@ -17,6 +17,19 @@ use revive_dt_common::macros::define_wrapper_type;
 use crate::traits::ResolverApi;
 use crate::{metadata::ContractInstance, traits::ResolutionContext};
 
+/// A test step.
+///
+/// A test step can be anything. It could be an invocation to a function, an assertion, or any other
+/// action that needs to be run or executed on the nodes used in the tests.
+#[derive(Clone, Debug, Serialize, Deserialize, Eq, PartialEq)]
+#[serde(untagged)]
+pub enum Step {
+    /// A function call or an invocation to some function on some smart contract.
+    FunctionCall(Box<Input>),
+    /// A step for performing a balance assertion on some account or contract.
+    BalanceAssertion(Box<BalanceAssertion>),
+}
+
 #[derive(Clone, Debug, Default, Serialize, Deserialize, Eq, PartialEq)]
 pub struct Input {
     #[serde(default = "Input::default_caller")]
@@ -33,6 +46,20 @@ pub struct Input {
     pub variable_assignments: Option<VariableAssignments>,
 }
 
+#[derive(Clone, Debug, Default, Serialize, Deserialize, Eq, PartialEq)]
+pub struct BalanceAssertion {
+    /// The address that the balance assertion should be done on.
+    ///
+    /// This is a string which will be resolved into an address when being processed. Therefore,
+    /// this could be a normal hex address, a variable such as `Test.address`, or perhaps even a
+    /// full on variable like `$VARIABLE:Uniswap`. It follows the same resolution rules that are
+    /// followed in the calldata.
+    pub address: String,
+
+    /// The amount of balance to assert that the account or contract has.
+    pub expected_balance: U256,
+}
+
 #[derive(Clone, Debug, Serialize, Deserialize, Eq, PartialEq)]
 #[serde(untagged)]
 pub enum Expected {