refactor(tests): modularize

tests/common.rs

@@ -0,0 +1,27 @@
+use captra::{CapabilityManifest, HostState, add_wasm_linker_funcs, load_manifest};
+use ed25519_dalek::SigningKey;
+use rand::rngs::OsRng;
+use wasmtime::{Engine, Linker, Store};
+
+/// Load the example manifest bundled with the repo.
+pub fn load_example_manifest() -> CapabilityManifest {
+    load_manifest("examples/manifest.json").expect("examples/manifest.json must exists")
+}
+
+/// Build a HostState with a fixed seed and a fresh SigningKey (OsRng).
+pub fn make_host_with_seed(seed: u64) -> HostState {
+    let manifest = load_example_manifest();
+    let mut csprng = OsRng;
+    let keypair = SigningKey::generate(&mut csprng);
+    HostState::new(manifest, seed, keypair)
+}
+
+/// Create a wasmtime engine + linker with your host functions registered,
+/// and a Store that owns the given HostState.
+pub fn wasm_store_with_hosts(host: HostState) -> (Engine, Linker<HostState>, Store<HostState>) {
+    let engine = Engine::default();
+    let mut linker = Linker::new(&engine);
+    add_wasm_linker_funcs(&mut linker).expect("linker registration");
+    let store = Store::new(&engine, host);
+    (engine, linker, store)
+}