fix(fuzz): do not exceed configured runs (#7971)

* fix(fuzz): do not exceed configured runs

* Add test

crates/forge/src/lib.rs

@@ -149,6 +149,9 @@ impl TestOptions {
             failure_persistence: file_failure_persistence,
             cases,
             max_global_rejects: self.fuzz.max_test_rejects,
+            // Disable proptest shrink: for fuzz tests we provide single counterexample,
+            // for invariant tests we shrink outside proptest.
+            max_shrink_iters: 0,
             ..Default::default()
         };
 

crates/forge/tests/cli/test_cmd.rs

@@ -1,6 +1,7 @@
 //! Contains various tests for `forge test`.
 
-use foundry_config::Config;
+use alloy_primitives::U256;
+use foundry_config::{Config, FuzzConfig};
 use foundry_test_utils::{
     rpc,
     util::{OutputExt, OTHER_SOLC_VERSION, SOLC_VERSION},
@@ -544,3 +545,51 @@ contract Dummy {
     cmd.args(["test", "--match-path", "src/dummy.sol"]);
     cmd.assert_success()
 });
+
+forgetest_init!(should_not_shrink_fuzz_failure, |prj, cmd| {
+    prj.wipe_contracts();
+
+    // deterministic test so we always have 54 runs until test fails with overflow
+    let config = Config {
+        fuzz: { FuzzConfig { runs: 256, seed: Some(U256::from(100)), ..Default::default() } },
+        ..Default::default()
+    };
+    prj.write_config(config);
+
+    prj.add_test(
+        "CounterFuzz.t.sol",
+        r#"pragma solidity 0.8.24;
+import {Test} from "forge-std/Test.sol";
+
+contract Counter {
+    uint256 public number = 0;
+
+    function addOne(uint256 x) external pure returns (uint256) {
+        return x + 100_000_000;
+    }
+}
+
+contract CounterTest is Test {
+    Counter public counter;
+
+    function setUp() public {
+        counter = new Counter();
+    }
+
+    function testAddOne(uint256 x) public view {
+        assertEq(counter.addOne(x), x + 100_000_000);
+    }
+}
+     "#,
+    )
+    .unwrap();
+
+    cmd.args(["test"]);
+    let (stderr, _) = cmd.unchecked_output_lossy();
+    let runs = stderr.find("runs:").and_then(|start_runs| {
+        let runs_split = &stderr[start_runs + 6..];
+        runs_split.find(',').map(|end_runs| &runs_split[..end_runs])
+    });
+    // make sure there are only 54 runs (with proptest shrinking same test results in 292 runs)
+    assert_eq!(runs.unwrap().parse::<usize>().unwrap(), 54);
+});