Get a basic first test working, and lots of changes to supporting code to facilitate this

backend/test_utils/src/server/default_commands.rs

@@ -0,0 +1,30 @@
+use super::Command;
+use std::path::PathBuf;
+
+pub fn default_telemetry_shard_command() -> Result<Command, std::io::Error> {
+    default_telemetry_command("telemetry_shard")
+}
+
+pub fn default_telemetry_core_command() -> Result<Command, std::io::Error> {
+    default_telemetry_command("telemetry_core")
+}
+
+fn default_telemetry_command(bin: &'static str) -> Result<Command, std::io::Error> {
+    let mut workspace_dir = try_find_workspace_dir()?;
+    workspace_dir.push("Cargo.toml");
+    Ok(Command::new("cargo")
+        .arg("run")
+        .arg("--bin")
+        .arg(bin)
+        .arg("--manifest-path")
+        .arg(workspace_dir)
+        .arg("--"))
+}
+
+/// A _very_ naive way to find the workspace ("backend") directory
+/// from the current path (which is assumed to be inside it).
+fn try_find_workspace_dir() -> Result<PathBuf, std::io::Error> {
+    let mut dir = std::env::current_dir()?;
+    while !dir.ends_with("backend") && dir.pop() {}
+    Ok(dir)
+}