Replace the test added by #349 with a bench (#351)

CI environments can be noisy and while the test worked great
locally on my machine, it didn't on the CI environment.
This replaces the test with a (manually tracked) benchmark.
As per https://github.com/alexcrichton/toml-rs/pull/349#issuecomment-546998173

.github/workflows/main.yml

@@ -15,6 +15,7 @@ jobs:
     - run: cargo test
     - run: cargo test --features preserve_order
     - run: cargo test --manifest-path test-suite/Cargo.toml
+    - run: cargo bench
 
   rustfmt:
     name: Rustfmt

test-suite/Cargo.toml

@@ -5,7 +5,12 @@ authors = ["Alex Crichton <alex@alexcrichton.com>"]
 publish = false
 edition = "2018"
 
+[[bench]]
+name = "linear"
+harness = false
+
 [dev-dependencies]
+bencher = "0.1"
 toml = { path = ".." }
 serde = { version = "1.0", features = ["derive"] }
 serde_derive = "1.0"

test-suite/benches/linear.rs

@@ -0,0 +1,35 @@
+// Regressoion test for https://github.com/alexcrichton/toml-rs/issues/342
+
+use bencher::{benchmark_group, benchmark_main, black_box, Bencher};
+use toml::Value;
+
+fn parse(bench: &mut Bencher, entries: usize, f: impl Fn(usize) -> String) {
+    let mut s = String::new();
+    for i in 0..entries {
+        s += &f(i);
+        s += "entry = 42\n"
+    }
+    let s = black_box(s);
+    bench.iter(|| {
+        black_box(s.parse::<Value>().unwrap());
+    })
+}
+
+fn map_10(bench: &mut Bencher) {
+    parse(bench, 10, |i| format!("[header_no_{}]\n", i))
+}
+
+fn map_100(bench: &mut Bencher) {
+    parse(bench, 100, |i| format!("[header_no_{}]\n", i))
+}
+
+fn array_10(bench: &mut Bencher) {
+    parse(bench, 10, |_i| "[[header]]\n".to_owned())
+}
+
+fn array_100(bench: &mut Bencher) {
+    parse(bench, 100, |_i| "[[header]]\n".to_owned())
+}
+
+benchmark_group!(benches, map_10, map_100, array_10, array_100);
+benchmark_main!(benches);

test-suite/tests/linear.rs

@@ -1,37 +0,0 @@
-use std::time::{Duration, Instant};
-use toml::Value;
-
-const TOLERANCE: f64 = 2.0;
-
-fn measure_time(entries: usize, f: impl Fn(usize) -> String) -> Duration {
-    let start = Instant::now();
-    let mut s = String::new();
-    for i in 0..entries {
-        s += &f(i);
-        s += "entry = 42\n"
-    }
-    s.parse::<Value>().unwrap();
-    Instant::now() - start
-}
-
-#[test]
-fn linear_increase_map() {
-    let time_1 = measure_time(100, |i| format!("[header_no_{}]\n", i));
-    let time_4 = measure_time(400, |i| format!("[header_no_{}]\n", i));
-    dbg!(time_1, time_4);
-    // Now ensure that the deserialization time has increased linearly
-    // (within a tolerance interval) instead of, say, quadratically
-    assert!(time_4 > time_1.mul_f64(4.0 - TOLERANCE));
-    assert!(time_4 < time_1.mul_f64(4.0 + TOLERANCE));
-}
-
-#[test]
-fn linear_increase_array() {
-    let time_1 = measure_time(100, |i| format!("[[header_no_{}]]\n", i));
-    let time_4 = measure_time(400, |i| format!("[[header_no_{}]]\n", i));
-    dbg!(time_1, time_4);
-    // Now ensure that the deserialization time has increased linearly
-    // (within a tolerance interval) instead of, say, quadratically
-    assert!(time_4 > time_1.mul_f64(4.0 - TOLERANCE));
-    assert!(time_4 < time_1.mul_f64(4.0 + TOLERANCE));
-}