Make basic script a template, and add more assertions.

examples/acceptance_tests/062/validators/basic.ak

@@ -1,6 +1,43 @@
 use aiken/list
-use aiken/transaction.{ScriptContext}
+use aiken/option
+use aiken/transaction.{ScriptContext, Spend, TransactionId}
+use aiken/transaction/credential.{VerificationKeyCredential}
+use aiken/transaction/value
 
 fn spend(_datum: Void, _redeemer: Void, ctx: ScriptContext) {
-  list.length(ctx.transaction.outputs) == 1
+  [
+    assert_purpose(ctx.purpose),
+    assert_outputs(ctx.transaction),
+    assert_fee(ctx.transaction),
+  ]
+  |> list.and
+}
+
+fn assert_purpose(purpose) {
+  when purpose is {
+    Spend(ref) ->
+      ref.transaction_id == TransactionId(
+        #"0000000000000000000000000000000000000000000000000000000000000000",
+      ) && ref.output_index == 0
+    _ -> error("script purpose isn't 'Spend'")
+  }
+}
+
+fn assert_fee(transaction) {
+  transaction.fee == value.from_lovelace(42)
+}
+
+fn assert_outputs(transaction) {
+  when transaction.outputs is {
+    [output] ->
+      [
+        output.value == value.from_lovelace(1000000000),
+        output.address.payment_credential == VerificationKeyCredential(
+          #"11111111111111111111111111111111111111111111111111111111",
+        ),
+        option.is_none(output.address.stake_credential),
+      ]
+      |> list.and
+    _ -> error("unexpected number of outputs")
+  }
 }