spirv-builder: clap testing

Author: Firestar99

.github/workflows/ci.yaml

@@ -54,7 +54,7 @@ jobs:
         run: cargo test -p rustc_codegen_spirv --release --no-default-features --features "use-installed-tools"
 
       - name: workspace test (excluding examples & difftest)
-        run: cargo test --release --workspace --exclude "example-runner-*" --exclude "difftest*" --no-default-features --features "use-installed-tools"
+        run: cargo test --release --workspace --exclude "example-runner-*" --exclude "difftest*" --no-default-features --features "use-installed-tools,clap"
 
       # Examples
       - name: cargo check examples

crates/spirv-builder/src/lib.rs

@@ -73,6 +73,8 @@
 
 pub mod cargo_cmd;
 mod depfile;
+#[cfg(test)]
+mod tests;
 #[cfg(feature = "watch")]
 mod watch;
 

crates/spirv-builder/src/tests.rs

@@ -0,0 +1,20 @@
+#[cfg(feature = "clap")]
+mod clap {
+    pub use crate::*;
+    use clap::Parser;
+
+    /// look at the output of this test to see what `--help` prints
+    #[test]
+    fn test_clap_help() {
+        // any malformed clap declarations should panic within clap's parse
+        match SpirvBuilder::try_parse_from(["", "--help"]) {
+            Ok(_) => panic!("`--help` should make clap return an error"),
+            Err(e) => {
+                let e = e.to_string();
+                println!("{}", e);
+                // sanity check help
+                assert!(e.contains("--target"));
+            }
+        };
+    }
+}