diff --git a/src/currentprocess.rs b/src/currentprocess.rs
index 115c678871..e9cfafa7d2 100644
--- a/src/currentprocess.rs
+++ b/src/currentprocess.rs
@@ -208,6 +208,16 @@ impl TestProcess {
         })
     }
 
+    /// Extracts the stdout from the process
+    pub fn stdout(&self) -> Vec<u8> {
+        let tp = match &self.process {
+            Process::TestProcess(tp) => tp,
+            _ => unreachable!(),
+        };
+
+        tp.stdout.lock().unwrap_or_else(|e| e.into_inner()).clone()
+    }
+
     /// Extracts the stderr from the process
     pub fn stderr(&self) -> Vec<u8> {
         let tp = match &self.process {
diff --git a/src/test/mock/clitools.rs b/src/test/mock/clitools.rs
index 9c3236fcb6..15a3986de5 100644
--- a/src/test/mock/clitools.rs
+++ b/src/test/mock/clitools.rs
@@ -16,8 +16,11 @@ use std::{
 
 use enum_map::{enum_map, Enum, EnumMap};
 use once_cell::sync::Lazy;
+use tokio::runtime::Builder;
 use url::Url;
 
+use crate::cli::rustup_mode;
+use crate::currentprocess;
 use crate::test as rustup_test;
 use crate::test::const_dist_dir;
 use crate::test::this_host_triple;
@@ -676,8 +679,13 @@ impl Config {
         I: IntoIterator<Item = A> + Clone + Debug,
         A: AsRef<OsStr>,
     {
+        let inprocess = allow_inprocess(name, args.clone());
         let start = Instant::now();
-        let out = self.run_subprocess(name, args.clone(), env);
+        let out = if inprocess {
+            self.run_inprocess(name, args.clone(), env)
+        } else {
+            self.run_subprocess(name, args.clone(), env)
+        };
         let duration = Instant::now() - start;
         let output = SanitizedOutput {
             ok: matches!(out.status, Some(0)),
@@ -686,6 +694,7 @@ impl Config {
         };
 
         println!("ran: {} {:?}", name, args);
+        println!("inprocess: {inprocess}");
         println!("status: {:?}", out.status);
         println!("duration: {:.3}s", duration.as_secs_f32());
         println!("stdout:\n====\n{}\n====\n", output.stdout);
@@ -694,6 +703,55 @@ impl Config {
         output
     }
 
+    #[cfg_attr(feature = "otel", tracing::instrument(skip_all))]
+    pub(crate) fn run_inprocess<I, A>(&self, name: &str, args: I, env: &[(&str, &str)]) -> Output
+    where
+        I: IntoIterator<Item = A>,
+        A: AsRef<OsStr>,
+    {
+        // should we use vars_os, or skip over non-stringable vars? This is test
+        // code after all...
+        let mut vars: HashMap<String, String> = HashMap::default();
+        self::env(self, &mut vars);
+        vars.extend(env.iter().map(|(k, v)| (k.to_string(), v.to_string())));
+        let mut arg_strings: Vec<Box<str>> = Vec::new();
+        arg_strings.push(name.to_owned().into_boxed_str());
+        for arg in args {
+            arg_strings.push(
+                arg.as_ref()
+                    .to_os_string()
+                    .into_string()
+                    .unwrap()
+                    .into_boxed_str(),
+            );
+        }
+        let mut builder = Builder::new_multi_thread();
+        builder
+            .enable_all()
+            .worker_threads(2)
+            .max_blocking_threads(2);
+        let rt = builder.build().unwrap();
+        rt.block_on(async {
+            let tp =
+                currentprocess::TestProcess::new(&*self.workdir.borrow(), &arg_strings, vars, "");
+            let process_res =
+                rustup_mode::main(tp.process.current_dir().unwrap(), &tp.process).await;
+            // convert Err's into an ec
+            let ec = match process_res {
+                Ok(process_res) => process_res,
+                Err(e) => {
+                    crate::cli::common::report_error(&e, &tp.process);
+                    utils::ExitCode(1)
+                }
+            };
+            Output {
+                status: Some(ec.0),
+                stderr: tp.stderr(),
+                stdout: tp.stdout(),
+            }
+        })
+    }
+
     #[track_caller]
     pub fn run_subprocess<I, A>(&self, name: &str, args: I, env: &[(&str, &str)]) -> Output
     where
@@ -797,6 +855,43 @@ pub fn env<E: rustup_test::Env>(config: &Config, cmd: &mut E) {
     config.env(cmd)
 }
 
+fn allow_inprocess<I, A>(name: &str, args: I) -> bool
+where
+    I: IntoIterator<Item = A>,
+    A: AsRef<OsStr>,
+{
+    // Only the rustup alias is currently ready for in-process testing:
+    // - -init performs self-update which monkey with global external state.
+    // - proxies themselves behave appropriately the proxied output needs to be
+    //   collected for assertions to be made on it as our tests traverse layers.
+    // - self update executions cannot run in-process because on windows the
+    //    process replacement dance would replace the test process.
+    // - any command with --version in it is testing to see something was
+    //   installed properly, so we have to shell out to it to be sure
+    if name != "rustup" {
+        return false;
+    }
+    let mut is_update = false;
+    let mut no_self_update = false;
+    let mut self_cmd = false;
+    let mut run = false;
+    let mut version = false;
+    for arg in args {
+        if arg.as_ref() == "update" {
+            is_update = true;
+        } else if arg.as_ref() == "--no-self-update" {
+            no_self_update = true;
+        } else if arg.as_ref() == "self" {
+            self_cmd = true;
+        } else if arg.as_ref() == "run" {
+            run = true;
+        } else if arg.as_ref() == "--version" {
+            version = true;
+        }
+    }
+    !(run || self_cmd || version || (is_update && !no_self_update))
+}
+
 #[derive(Copy, Clone, Eq, PartialEq)]
 enum RlsStatus {
     Available,