test: install binaries in the inst directory, run from there

This avoids having to determine the rigth path in the Cargo target
directory, which is tricky when --target is used.

Makefile

@@ -1,4 +1,25 @@
-TESTS = 
+# The "install_test" target installs the subplot binary so that
+# $(SUBPLOT) refers to it. This lets us run Subplot without invoking
+# "cargo run" every time. This means we invoke in a way that's more
+# natural and have to jump through fewer hoops. Also the binary can be
+# run from Python tests directly.
+
+SUBPLOT_DIR = $(abspath inst)
+
+# Individual tests run by `test` or `fast-test` targets.
+TESTS =
+
+# Set this to "--offline --locked" to build offline.
+OFFLINE = 
+
+# Cargo target architecture.
+TARGET =
+
+ifdef TARGET
+TARGET_ARG = --target $(TARGET)
+else
+TARGET_ARG =
+endif
 
 all: check build test doc shear
 
@@ -11,11 +32,17 @@ build:
 	cargo build --all-targets --workspace
 	subplot docgen ci-broker.subplot -o ci-broker.html
 
-fast-test: build
-	timeout 60 cargo test --workspace -- --skip upgrades $(TESTS)
+install_test_binary:
+	rm -rf "$(SUBPLOT_DIR)"
+	cargo install $(TARGET_ARG) --locked $(OFFLINE) --path=. --root="$(SUBPLOT_DIR)" --debug
+	mv "$(SUBPLOT_DIR)"/bin/* "$(SUBPLOT_DIR)"
+	rm -rf "$(SUBPLOT_DIR)"/.crate*  "$(SUBPLOT_DIR)"/bin
+
+fast-test: install_test_binary build
+	env SUBPLOT_DIR="$(SUBPLOT_DIR)" timeout 60 cargo test --workspace -- --skip upgrades $(TESTS)
 
 test: fast-test
-	timeout 300 cargo test --workspace -- $(TESTS)
+	env SUBPLOT_DIR="$(SUBPLOT_DIR)" timeout 300 cargo test --workspace -- $(TESTS)
 
 .PHONY: doc
 doc:

src/subplot.rs

@@ -383,11 +383,8 @@ fn head(rad_home: &Path, repo: &Path) -> Result<Oid, Box<dyn std::error::Error>>
 }
 
 fn bindir() -> PathBuf {
-    let path = if let Ok(target) = std::env::var("CARGO_TARGET_DIR") {
-        Path::new(&target).join("debug")
-    } else {
-        PathBuf::from("target/debug")
-    };
+    let path = std::env::var("SUBPLOT_DIR").expect("SUBPLOT_DIR must be set");
+    let path = Path::new(&path);
     path.canonicalize().unwrap()
 }