test: add basic fuzz

fuzz/.gitignore

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+target
+corpus
+artifacts
+coverage

fuzz/Cargo.toml

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+[package]
+name = "owned_ref_cell-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+
+[dependencies.owned_ref_cell]
+path = ".."
+
+[[bin]]
+name = "fuzz_basic_borrows"
+path = "fuzz_targets/fuzz_basic_borrows.rs"
+test = false
+doc = false
+bench = false

fuzz/fuzz_targets/fuzz_basic_borrows.rs

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+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+use owned_ref_cell::OwnedRefCell;
+use std::vec::Vec;
+
+fuzz_target!(|data: &[u8]| {
+    let cell = OwnedRefCell::new(0);
+    let mut immutable_borrows = Vec::new();
+    let mut mutable_borrows = Vec::new();
+
+    for &byte in data.iter() {
+        match byte % 3 {
+            0 => {
+                if let Some(borrow) = cell.try_borrow() {
+                    immutable_borrows.push(borrow); // hold the immutable borrow
+                }
+            }
+            1 => {
+                if let Some(mut borrow_mut) = cell.try_borrow_mut() {
+                    *borrow_mut += 1; // mutate the content
+                    mutable_borrows.push(borrow_mut); // hold the mutable borrow
+                }
+            }
+            _ => {
+                // Randomly drop borrows from both vectors
+                if !immutable_borrows.is_empty() {
+                    immutable_borrows.pop();
+                }
+                if !mutable_borrows.is_empty() {
+                    mutable_borrows.pop();
+                }
+            }
+        }
+    }
+});