docs: fix counter tutorial ownership semantics and add TXE tests

The counter tutorial framed the example as "your own private counter,"
but `increment(owner: AztecAddress)` let any caller mutate any owner's
counter. Drop the `owner` parameter and read `self.msg_sender()` so the
caller can only increment the counter mapped to their own address.

Also add a sibling `counter_contract_test` package (mirroring
`logging_example_test`) with TXE tests covering `initialize` and
`increment`. This catches regressions in the example contract via
`aztec test` when wired up.

Author: critesjosh

docs/Nargo.toml

@@ -2,6 +2,7 @@
 members = [
     "examples/circuits/hello_circuit",
     "examples/contracts/counter_contract",
+    "examples/contracts/counter_contract_test",
     "examples/contracts/bob_token_contract",
     "examples/contracts/nft",
     "examples/contracts/nft_bridge",

docs/docs-developers/docs/tutorials/contract_tutorials/counter_contract.md

@@ -118,7 +118,7 @@ Now let's implement an `increment` function to increase the counter.
 
 #include_code increment /docs/examples/contracts/counter_contract/src/main.nr rust
 
-The `increment` function works similarly to the `initialize` function. It logs a debug message, then adds 1 to the owner's counter and delivers the note onchain.
+The `increment` function uses `self.msg_sender()` so each caller can only increment the counter mapped to their own address. It logs a debug message, then adds 1 to that counter and delivers the note onchain.
 
 ## Getting a counter
 

docs/examples/contracts/counter_contract/src/main.nr

@@ -35,7 +35,8 @@ pub contract Counter {
 
     // docs:start:increment
     #[external("private")]
-    fn increment(owner: AztecAddress) {
+    fn increment() {
+        let owner = self.msg_sender();
         debug_log_format("Incrementing counter for owner {0}", [owner.to_field()]);
         self.storage.counters.at(owner).add(1).deliver(MessageDelivery.ONCHAIN_CONSTRAINED);
     }

docs/examples/contracts/counter_contract_test/Nargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "counter_contract_test"
+authors = [""]
+compiler_version = ">=0.25.0"
+type = "lib"
+
+[dependencies]
+aztec = { path = "../../../../noir-projects/aztec-nr/aztec" }
+balance_set = { path = "../../../../noir-projects/aztec-nr/balance-set" }
+counter_contract = { path = "../counter_contract" }

docs/examples/contracts/counter_contract_test/src/lib.nr

@@ -0,0 +1,32 @@
+use counter_contract::Counter;
+use aztec::{protocol::address::AztecAddress, test::helpers::test_environment::TestEnvironment};
+
+pub unconstrained fn setup(headstart: u128) -> (TestEnvironment, AztecAddress, AztecAddress) {
+    let mut env = TestEnvironment::new();
+    let owner = env.create_light_account();
+
+    let initializer = Counter::interface().initialize(headstart, owner);
+    let contract_address =
+        env.deploy("@counter_contract/Counter").with_private_initializer(owner, initializer);
+    (env, contract_address, owner)
+}
+
+#[test]
+unconstrained fn test_initialize_sets_headstart() {
+    let headstart = 5;
+    let (env, contract_address, owner) = setup(headstart);
+
+    let value = env.execute_utility(Counter::at(contract_address).get_counter(owner));
+    assert(value == headstart, "initial counter should equal headstart");
+}
+
+#[test]
+unconstrained fn test_increment_increases_caller_counter() {
+    let headstart = 5;
+    let (mut env, contract_address, owner) = setup(headstart);
+
+    env.call_private(owner, Counter::at(contract_address).increment());
+
+    let value = env.execute_utility(Counter::at(contract_address).get_counter(owner));
+    assert(value == headstart + 1, "counter should be incremented by 1");
+}