diff --git a/build_tool/lib/src/util.dart b/build_tool/lib/src/util.dart
index 15cde67..d8e3019 100644
--- a/build_tool/lib/src/util.dart
+++ b/build_tool/lib/src/util.dart
@@ -37,6 +37,44 @@ class CommandFailedException implements Exception {
   }
 }
 
+class TestRunCommandArgs {
+  final String executable;
+  final List<String> arguments;
+  final String? workingDirectory;
+  final Map<String, String>? environment;
+  final bool includeParentEnvironment;
+  final bool runInShell;
+  final Encoding? stdoutEncoding;
+  final Encoding? stderrEncoding;
+
+  TestRunCommandArgs({
+    required this.executable,
+    required this.arguments,
+    this.workingDirectory,
+    this.environment,
+    this.includeParentEnvironment = true,
+    this.runInShell = false,
+    this.stdoutEncoding,
+    this.stderrEncoding,
+  });
+}
+
+class TestRunCommandResult {
+  TestRunCommandResult({
+    this.pid = 1,
+    this.exitCode = 0,
+    this.stdout = '',
+    this.stderr = '',
+  });
+
+  final int pid;
+  final int exitCode;
+  final String stdout;
+  final String stderr;
+}
+
+TestRunCommandResult Function(TestRunCommandArgs args)? testRunCommandOverride;
+
 ProcessResult runCommand(
   String executable,
   List<String> arguments, {
@@ -47,6 +85,24 @@ ProcessResult runCommand(
   Encoding? stdoutEncoding = systemEncoding,
   Encoding? stderrEncoding = systemEncoding,
 }) {
+  if (testRunCommandOverride != null) {
+    final result = testRunCommandOverride!(TestRunCommandArgs(
+      executable: executable,
+      arguments: arguments,
+      workingDirectory: workingDirectory,
+      environment: environment,
+      includeParentEnvironment: includeParentEnvironment,
+      runInShell: runInShell,
+      stdoutEncoding: stdoutEncoding,
+      stderrEncoding: stderrEncoding,
+    ));
+    return ProcessResult(
+      result.pid,
+      result.exitCode,
+      result.stdout,
+      result.stderr,
+    );
+  }
   log.finer('Running command $executable ${arguments.join(' ')}');
   final res = Process.runSync(
     _resolveExecutable(executable),
diff --git a/build_tool/test/rustup_test.dart b/build_tool/test/rustup_test.dart
new file mode 100644
index 0000000..af95303
--- /dev/null
+++ b/build_tool/test/rustup_test.dart
@@ -0,0 +1,66 @@
+import 'package:build_tool/src/rustup.dart';
+import 'package:build_tool/src/util.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('rustup with no toolchains', () {
+    bool didListToolchains = false;
+    bool didInstallStable = false;
+    bool didListTargets = false;
+    testRunCommandOverride = (args) {
+      expect(args.executable, 'rustup');
+      switch (args.arguments) {
+        case ['toolchain', 'list']:
+          didListToolchains = true;
+          return TestRunCommandResult(stdout: 'no installed toolchains\n');
+        case ['toolchain', 'install', 'stable']:
+          didInstallStable = true;
+          return TestRunCommandResult();
+        case ['target', 'list', '--toolchain', 'stable', '--installed']:
+          didListTargets = true;
+          return TestRunCommandResult(
+              stdout: 'x86_64-unknown-linux-gnu\nx86_64-apple-darwin\n');
+        default:
+          throw Exception('Unexpected call: ${args.arguments}');
+      }
+    };
+    final rustup = Rustup();
+    rustup.installToolchain('stable');
+    expect(didInstallStable, true);
+    expect(didListToolchains, true);
+    expect(didListTargets, true);
+    expect(rustup.installedTargets('stable'), [
+      'x86_64-unknown-linux-gnu',
+      'x86_64-apple-darwin',
+    ]);
+    testRunCommandOverride = null;
+  });
+
+  test('rustup with esp toolchain', () {
+    final targetsQueried = <String>[];
+    testRunCommandOverride = (args) {
+      expect(args.executable, 'rustup');
+      switch (args.arguments) {
+        case ['toolchain', 'list']:
+          return TestRunCommandResult(
+              stdout: 'stable-aarch64-apple-darwin (default)\n'
+                  'nightly-aarch64-apple-darwin\n'
+                  'esp\n');
+        case ['target', 'list', '--toolchain', String toolchain, '--installed']:
+          targetsQueried.add(toolchain);
+          return TestRunCommandResult(stdout: '$toolchain:target\n');
+        default:
+          throw Exception('Unexpected call: ${args.arguments}');
+      }
+    };
+    final rustup = Rustup();
+    expect(targetsQueried, [
+      'stable-aarch64-apple-darwin',
+      'nightly-aarch64-apple-darwin',
+    ]);
+    expect(rustup.installedTargets('stable'),
+        ['stable-aarch64-apple-darwin:target']);
+    expect(rustup.installedTargets('nightly'),
+        ['nightly-aarch64-apple-darwin:target']);
+  });
+}