diff --git a/Package.swift b/Package.swift
index 3703ea5..e611a71 100644
--- a/Package.swift
+++ b/Package.swift
@@ -11,12 +11,12 @@ let package = Package(
   ],
   dependencies: [
     .package(url: "https://github.com/onevcat/Rainbow.git", from: "3.0.0"),
-    .package(url: "https://github.com/JohnSundell/ShellOut.git", from: "2.1.0"),
+    .package(url: "https://github.com/apple/swift-package-manager.git", from: "0.1.0"),
   ],
   targets: [
     .target(
       name: "LiteSupport",
-      dependencies: ["Rainbow", "ShellOut"]),
+      dependencies: ["Rainbow", "Utility"]),
 
     // This needs to be named `lite-test` instead of `lite` because consumers
     // of `lite` should use the target name `lite`.
diff --git a/Sources/LiteSupport/ParallelExecutor.swift b/Sources/LiteSupport/ParallelExecutor.swift
index 0eab4b4..1583fb7 100644
--- a/Sources/LiteSupport/ParallelExecutor.swift
+++ b/Sources/LiteSupport/ParallelExecutor.swift
@@ -60,7 +60,7 @@ final class ParallelExecutor<TaskResult> {
   /// Adds a task to run asynchronously on the next worker. Workers are chosen
   /// in a round-robin fashion.
   func addTask(_ work: @escaping () -> TaskResult) {
-    queues[nextTask % queues.count].async(group: group) {
+    queues[nextTask % queues.count].async(group: group, qos: .userInitiated) {
       self.addResult(work())
     }
   }
diff --git a/Sources/LiteSupport/TestRunner.swift b/Sources/LiteSupport/TestRunner.swift
index 35e608d..3b3c73a 100644
--- a/Sources/LiteSupport/TestRunner.swift
+++ b/Sources/LiteSupport/TestRunner.swift
@@ -7,7 +7,9 @@
 
 import Foundation
 import Rainbow
-import ShellOut
+import Basic
+import Utility
+import POSIX
 import Dispatch
 
 /// Specifies how to parallelize test runs.
@@ -36,7 +38,7 @@ public enum ParallelismLevel {
 class TestRunner {
 
   /// The test directory in which tests reside.
-  let testDir: URL
+  let testDir: Foundation.URL
 
   /// The set of substitutions to apply to each run line.
   let substitutor: Substitutor
@@ -92,7 +94,7 @@ class TestRunner {
     let enumerator = fm.enumerator(at: testDir,
                                    includingPropertiesForKeys: nil)!
     var files = [TestFile]()
-    for case let file as URL in enumerator {
+    for case let file as Foundation.URL in enumerator {
       guard pathExtensions.contains(file.pathExtension) else { continue }
       let nsPath = NSString(string: file.path)
       let matchesFilter = filters.contains {
@@ -250,15 +252,26 @@ class TestRunner {
       let exitCode: Int
       let bash = file.makeCommandLine(line, substitutor: substitutor)
       do {
-        stdout = try shellOut(to: bash)
+        let args = bash.split(separator: " ").map { String($0 as Substring) }
+        let result = try Process.popen(arguments: args)
+        stdout = try result.utf8Output().chomp()
         stderr = ""
-        exitCode = 0
-      } catch let error as ShellOutError {
-        stderr = error.message
-        stdout = error.output
-        exitCode = Int(error.terminationStatus)
+        switch result.exitStatus {
+        case let .terminated(code: code):
+          exitCode = Int(code)
+        case let .signalled(signal: code):
+          exitCode = Int(code)
+        }
+      } catch let error as SystemError {
+        stderr = error.description
+        stdout = ""
+        exitCode = Int(error.exitCode)
+      } catch let error as Basic.Process.Error {
+        stderr = error.description
+        stdout = ""
+        exitCode = Int(EXIT_FAILURE)
       } catch {
-        fatalError("unhandled error")
+        fatalError("\(error)")
       }
       let end = Date()
       results.append(TestResult(line: line,
@@ -271,3 +284,60 @@ class TestRunner {
     return results
   }
 }
+
+extension SystemError {
+  var exitCode: Int32 {
+    switch self {
+    case .chdir(let errno, _):
+      return errno
+    case .close(let errno):
+      return errno
+    case .dirfd(let errno, _):
+      return errno
+    case .exec(let errno, _, _):
+      return errno
+    case .fgetc(let errno):
+      return errno
+    case .fread(let errno):
+      return errno
+    case .getcwd(let errno):
+      return errno
+    case .mkdir(let errno, _):
+      return errno
+    case .mkdtemp(let errno):
+      return errno
+    case .pipe(let errno):
+      return errno
+    case .posix_spawn(let errno, _):
+      return errno
+    case .popen(let errno, _):
+      return errno
+    case .read(let errno):
+      return errno
+    case .readdir(let errno, _):
+      return errno
+    case .realpath(let errno, _):
+      return errno
+    case .rename(let errno, _, _):
+      return errno
+    case .rmdir(let errno, _):
+      return errno
+    case .setenv(let errno, _):
+      return errno
+    case .stat(let errno, _):
+      return errno
+    case .symlink(let errno, _, _):
+      return errno
+    case .symlinkat(let errno, _):
+      return errno
+    case .unlink(let errno, _):
+      return errno
+    case .unsetenv(let errno, _):
+      return errno
+    case .waitpid(let errno):
+      return errno
+    case .usleep(let errno):
+      return errno
+    }
+  }
+}