test: add Subplot scenario for a smoke test

Sponsored-by: author

3 files changed, 53 insertions, 6 deletions

diff --git a/obnam-benchmark.md b/obnam-benchmark.md
index 076255d..709260d 100644
--- a/obnam-benchmark.md
+++ b/obnam-benchmark.md
@@ -115,3 +115,24 @@ benchmarks:
 }
 ```
 
+
+## Smoke test to run a trivial benchmark
+
+_Requirement: The benchmark tool can benchmarks at all._
+
+We verify this by running a trivial benchmark, which backs up an
+empty directory.
+
+~~~scenario
+given an installed Rust program obnam-benchmark
+given file smoke.yaml
+when I run obnam-benchmark run smoke.yaml --output smoke.json
+then file smoke.json is valid JSON
+~~~
+
+```{#smoke.yaml .yaml .file .numberLines}
+benchmarks:
+- benchmark: smoke
+  backups:
+  - changes: []
+```
diff --git a/subplot/benchmark.rs b/subplot/benchmark.rs
index 7ea4a94..566ce30 100644
--- a/subplot/benchmark.rs
+++ b/subplot/benchmark.rs
@@ -33,13 +33,15 @@ fn install_rust_program(context: &ScenarioContext) {
 fn json_files_match(context: &ScenarioContext, first: &str, second: &str) {
     context.with(
         |context: &Datadir| {
-            let first = context.canonicalise_filename(&first).expect("can't use first filename");
-            let first = File::open(&first)?;
-            let first: Value = serde_json::from_reader(&first)?;
+            let first = context
+                .canonicalise_filename(&first)
+                .expect("can't use first filename");
+            let first = read_json_file(&first)?;
 
-            let second = context.canonicalise_filename(&second).expect("can't use second filename");
-            let second = File::open(&second)?;
-            let second: Value = serde_json::from_reader(&second)?;
+            let second = context
+                .canonicalise_filename(&second)
+                .expect("can't use second filename");
+            let second = read_json_file(&second)?;
 
             if first != second {
                 eprintln!("JSON files differ:\n{:#?}\n\n{:#?}\n", first, second,);
@@ -51,3 +53,22 @@ fn json_files_match(context: &ScenarioContext, first: &str, second: &str) {
         false,
     );
 }
+
+#[step]
+#[context(Datadir)]
+#[context(SubplotContext)]
+fn file_is_valid_json(context: &ScenarioContext, filename: &str) {
+    context.with(
+        |context: &Datadir| {
+            let filename = context.canonicalise_filename(&filename)?;
+            read_json_file(&filename)?;
+            Ok(())
+        },
+        false,
+    )?;
+}
+
+fn read_json_file(filename: &Path) -> anyhow::Result<Value> {
+    let file = File::open(filename)?;
+    Ok(serde_json::from_reader(&file)?)
+}
diff --git a/subplot/benchmark.yaml b/subplot/benchmark.yaml
index b0e6727..70ebb54 100644
--- a/subplot/benchmark.yaml
+++ b/subplot/benchmark.yaml
@@ -7,3 +7,8 @@
   impl:
     rust:
       function: json_files_match
+
+- then: file {filename} is valid JSON
+  impl:
+    rust:
+      function: file_is_valid_json