Add error message to README

README.md

@@ -14,10 +14,10 @@ async fn test() {
     expect!(1..=5, count, to_equal(5));
 
     expect!(
-        [get_cat_url(0), get_cat_url(5), get_cat_url(42)],
+        [get_cat_url(0), get_cat_url(40), get_cat_url(42)],
         all,
         when_ready,
-        to_end_with(".png"),
+        to_end_with("0.png"),
     ).await;
 }
 
@@ -26,6 +26,29 @@ async fn get_cat_url(id: u32) -> String {
 }
 ```
 
+Error message:
+
+```text
+thread 'test' panicked at README.md:13:6:
+assertion failed:
+  at: README.md:8:5 [readme_example]
+  subject: [get_cat_url(0), get_cat_url(40), get_cat_url(42)]
+
+steps:
+  all:
+    received: ? (no debug representation)
+    index: 2
+
+  when_ready:
+    received: ? (no debug representation)
+
+  to_end_with: substring not found
+    received: "cats/42.png"
+    expected: "0.png"
+```
+
+Supports colored messages with the `colors` feature.
+
 ## Built-in assertions
 
 ### General

tests/readme_example.rs

@@ -0,0 +1,20 @@
+use expecters::prelude::*;
+
+#[tokio::test]
+#[ignore = "run this manually to see the output from the README"]
+async fn test() {
+    expect!(1, as_display, to_equal("1"));
+    expect!(1..=5, count, to_equal(5));
+
+    expect!(
+        [get_cat_url(0), get_cat_url(40), get_cat_url(42)],
+        all,
+        when_ready,
+        to_end_with("0.png"),
+    )
+    .await;
+}
+
+async fn get_cat_url(id: u32) -> String {
+    format!("cats/{id}.png")
+}