value not must be null

README.md

@@ -13,15 +13,13 @@ Expression examples look like this:
 
 ````md
 ```nix
-assert 1 + 1 == 2; null
+let n = 1 + 1; in assert n == 2; n
 ```
 ````
 
 They are nix expressions inside of fenced code blocks.
 The first word in their info string is `nix`.
 The expression is passed to Nix for evaluation as `nix eval --expr <EXPRESSION>`.
-For future compatibility, to be considered passing,
-it must successfully evaluate into `null`.
 It is expected of the author to demonstrate and prove their points
 using assertions.
 

src/app/state.rs

@@ -2,7 +2,6 @@ pub(crate) mod expression_state;
 pub(crate) mod repl_state;
 
 use anyhow::bail;
-use indoc::formatdoc;
 
 use crate::{
     example_id::ExampleId,
@@ -269,19 +268,6 @@ impl State {
             bail!("{example_id}\n{stderr}")
         }
 
-        if expression_output.stdout != b"null\n" {
-            let stdout = String::from_utf8_lossy(&expression_output.stdout);
-            let stdout = stdout.trim_end();
-
-            let message = formatdoc! {"
-                {example_id}
-                evaluated into non-null
-                note: examples must evaluate into null
-                value: {stdout}"};
-
-            bail!("{message}");
-        }
-
         self.examples.remove(&example_id)?;
 
         Ok(vec![self.eprintln(Self::fmt_pass(&example_id))])

tests/expression.rs

@@ -1,7 +1,7 @@
 mod util;
 
 use assert_fs::fixture::FileWriteStr;
-use indoc::{formatdoc, indoc};
+use indoc::indoc;
 use predicates::{
     prelude::PredicateBooleanExt,
     str::{contains, starts_with},
@@ -27,42 +27,25 @@ fn assertion_fail() {
 }
 
 #[test]
-fn fail_non_null() {
+fn pass() {
     with_eelco(|file, eelco| {
         file.write_str(indoc! {"
                 ```nix
-                0
+                null
                 ```
-            "})
-            .unwrap();
-
-        let file_path = file.path().to_str().unwrap();
-
-        eelco.assert().failure().stderr(formatdoc! {"
-            Error: {file_path}:1
-            evaluated into non-null
-            note: examples must evaluate into null
-            value: 0
-        "});
-    });
-}
 
-#[test]
-fn pass() {
-    with_eelco(|file, eelco| {
-        file.write_str(indoc! {"
                 ```nix
-                null
+                0
                 ```
             "})
             .unwrap();
 
         let file_path = file.path().to_str().unwrap();
 
-        eelco
-            .assert()
-            .success()
-            .stderr(format!("PASS: {file_path}:1\n"));
+        eelco.assert().success().stderr(
+            predicates::str::contains(format!("PASS: {file_path}:1\n"))
+                .and(predicates::str::contains(format!("PASS: {file_path}:5\n"))),
+        );
     });
 }