diff --git a/src/main.ts b/src/main.ts
index 004152d..88fbfec 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -3,7 +3,7 @@ import {type Readable} from 'node:stream';
 import {normalize as normalizePath} from 'node:path';
 import {cwd as getCwd} from 'node:process';
 import {computeEnv} from './env.js';
-import {readStreamAsString, combineStreams} from './stream.js';
+import {combineStreams} from './stream.js';
 import readline from 'node:readline';
 
 export interface Output {
@@ -156,24 +156,24 @@ export class ExecProcess implements Result {
 
   async *[Symbol.asyncIterator](): AsyncIterator<string> {
     const proc = this._process;
+
     if (!proc) {
       return;
     }
 
-    if (this._thrownError) {
-      throw this._thrownError;
-    }
+    const streams: Readable[] = [];
 
-    const sources: Readable[] = [];
-    if (proc.stderr) {
-      sources.push(proc.stderr);
+    if (this._streamErr) {
+      streams.push(this._streamErr);
     }
-    if (proc.stdout) {
-      sources.push(proc.stdout);
+    if (this._streamOut) {
+      streams.push(this._streamOut);
     }
-    const combined = combineStreams(sources);
+
+    const streamCombined = combineStreams(streams);
+
     const rl = readline.createInterface({
-      input: combined
+      input: streamCombined
     });
 
     for await (const chunk of rl) {
@@ -181,6 +181,12 @@ export class ExecProcess implements Result {
     }
 
     await this._processClosed;
+
+    proc.removeAllListeners();
+
+    if (this._thrownError) {
+      throw this._thrownError;
+    }
   }
 
   protected async _waitForOutput(): Promise<Output> {
@@ -194,6 +200,21 @@ export class ExecProcess implements Result {
       throw new Error('No process was started');
     }
 
+    let stderr = '';
+    let stdout = '';
+
+    if (this._streamErr) {
+      for await (const chunk of this._streamErr) {
+        stderr += chunk.toString();
+      }
+    }
+
+    if (this._streamOut) {
+      for await (const chunk of this._streamOut) {
+        stdout += chunk.toString();
+      }
+    }
+
     await this._processClosed;
 
     proc.removeAllListeners();
@@ -202,14 +223,9 @@ export class ExecProcess implements Result {
       throw this._thrownError;
     }
 
-    const [stderr, stdout] = await Promise.all([
-      proc.stderr && readStreamAsString(proc.stderr),
-      proc.stdout && readStreamAsString(proc.stdout)
-    ]);
-
     const result: Output = {
-      stderr: stderr ?? '',
-      stdout: stdout ?? ''
+      stderr,
+      stdout
     };
 
     return result;
@@ -222,6 +238,9 @@ export class ExecProcess implements Result {
     return this._waitForOutput().then(onfulfilled, onrejected);
   }
 
+  protected _streamOut?: Readable;
+  protected _streamErr?: Readable;
+
   public spawn(): void {
     const cwd = getCwd();
     const options = this._options;
@@ -229,9 +248,10 @@ export class ExecProcess implements Result {
       ...defaultNodeOptions,
       ...options.nodeOptions
     };
-
     const signals: AbortSignal[] = [];
 
+    this._resetState();
+
     if (options.timeout !== undefined) {
       signals.push(AbortSignal.timeout(options.timeout));
     }
@@ -255,6 +275,13 @@ export class ExecProcess implements Result {
 
     const handle = spawn(normalisedCommand, normalisedArgs, nodeOptions);
 
+    if (handle.stderr) {
+      this._streamErr = handle.stderr;
+    }
+    if (handle.stdout) {
+      this._streamOut = handle.stdout;
+    }
+
     this._process = handle;
     handle.once('error', this._onError);
     handle.once('close', this._onClose);
@@ -267,6 +294,14 @@ export class ExecProcess implements Result {
     }
   }
 
+  protected _resetState(): void {
+    this._aborted = false;
+    this._processClosed = new Promise<void>((resolve) => {
+      this._resolveClose = resolve;
+    });
+    this._thrownError = undefined;
+  }
+
   protected _onError = (err: Error): void => {
     if (
       err.name === 'AbortError' &&
diff --git a/src/stream.ts b/src/stream.ts
index 6b4573f..b3e5684 100644
--- a/src/stream.ts
+++ b/src/stream.ts
@@ -1,26 +1,6 @@
 import {type EventEmitter} from 'node:events';
 import {type Readable, PassThrough} from 'node:stream';
 
-export const readStreamAsString = (stream: Readable): Promise<string> => {
-  return new Promise<string>((resolve, reject) => {
-    let result = '';
-    const onDataReceived = (chunk: Buffer | string): void => {
-      result += chunk.toString();
-    };
-
-    stream.once('error', (err) => {
-      reject(err);
-    });
-
-    stream.on('data', onDataReceived);
-
-    stream.once('end', () => {
-      stream.removeListener('data', onDataReceived);
-      resolve(result);
-    });
-  });
-};
-
 export const waitForEvent = (
   emitter: EventEmitter,
   name: string
diff --git a/src/test/main_test.ts b/src/test/main_test.ts
new file mode 100644
index 0000000..8b6a0d0
--- /dev/null
+++ b/src/test/main_test.ts
@@ -0,0 +1,98 @@
+import {x} from '../main.js';
+import * as assert from 'node:assert/strict';
+import {test} from 'node:test';
+
+test('exec', async (t) => {
+  await t.test('resolves to stdout', async () => {
+    const result = await x('echo', ['foo']);
+    assert.equal(result.stdout, 'foo\n');
+    assert.equal(result.stderr, '');
+  });
+
+  await t.test('times out after defined timeout (ms)', async () => {
+    const proc = x('sleep', ['0.2s'], {timeout: 100});
+    await assert.rejects(async () => {
+      await proc;
+    });
+    assert.equal(proc.killed, true);
+    assert.equal(proc.process!.signalCode, 'SIGTERM');
+  });
+
+  await t.test('throws spawn errors', async () => {
+    const proc = x('definitelyNonExistent');
+    await assert.rejects(async () => {
+      await proc;
+    }, 'spawn definitelyNonExistent NOENT');
+  });
+
+  await t.test('captures stderr', async () => {
+    const result = await x('cat', ['nonexistentforsure']);
+    assert.equal(
+      result.stderr,
+      'cat: nonexistentforsure: No such file or directory\n'
+    );
+    assert.equal(result.stdout, '');
+  });
+
+  await t.test('pid is number', async () => {
+    const proc = x('echo', ['foo']);
+    await proc;
+    assert.ok(typeof proc.pid === 'number');
+  });
+
+  await t.test('exitCode is set correctly', async () => {
+    const proc = x('echo', ['foo']);
+    assert.equal(proc.exitCode, undefined);
+    await proc;
+    assert.equal(proc.exitCode, 0);
+  });
+
+  await t.test('kill terminates the process', async () => {
+    const proc = x('sleep', ['5s']);
+    const result = proc.kill();
+    assert.ok(result);
+    assert.ok(proc.killed);
+    assert.equal(proc.aborted, false);
+  });
+
+  await t.test('pipe correctly pipes output', async () => {
+    const echoProc = x('echo', ['foo\nbar']);
+    const grepProc = echoProc.pipe('grep', ['foo']);
+    const result = await grepProc;
+
+    assert.equal(result.stderr, '');
+    assert.equal(result.stdout, 'foo\n');
+    assert.equal(echoProc.exitCode, 0);
+    assert.equal(grepProc.exitCode, 0);
+  });
+
+  await t.test('async iterator gets correct output', async () => {
+    const proc = x('echo', ['foo\nbar']);
+    const lines = [];
+    for await (const line of proc) {
+      lines.push(line);
+    }
+
+    assert.deepEqual(lines, ['foo', 'bar']);
+  });
+
+  await t.test('async iterator receives errors', async () => {
+    const proc = x('nonexistentforsure');
+    await assert.rejects(async () => {
+      for await (const line of proc) {
+        line;
+      }
+    });
+  });
+
+  await t.test('signal can be used to abort execution', async () => {
+    const controller = new AbortController();
+    const proc = x('sleep', ['4s'], {signal: controller.signal});
+    controller.abort();
+    const result = await proc;
+    assert.ok(proc.aborted);
+    assert.ok(proc.killed);
+    assert.equal(result.stderr, '');
+    assert.equal(result.stdout, '');
+  });
+});
diff --git a/src/test/stream_test.ts b/src/test/stream_test.ts
index cc29ed5..fa7feaf 100644
--- a/src/test/stream_test.ts
+++ b/src/test/stream_test.ts
@@ -1,4 +1,4 @@
-import {combineStreams, waitForEvent, readStreamAsString} from '../stream.js';
+import {combineStreams, waitForEvent} from '../stream.js';
 import * as assert from 'node:assert/strict';
 import {test} from 'node:test';
 import {EventEmitter} from 'node:events';
@@ -13,36 +13,6 @@ test('waitForEvent', async (t) => {
   });
 });
 
-test('readStreamAsString', async (t) => {
-  await t.test('rejects on error', async () => {
-    const streamError = new Error('fudge');
-    const stream = new Readable({
-      read() {
-        this.destroy(streamError);
-      }
-    });
-    await assert.rejects(readStreamAsString(stream), streamError);
-  });
-
-  await t.test('resolves to concatenated data', async () => {
-    const stream = Readable.from(['foo', 'bar']);
-    const result = await readStreamAsString(stream);
-    assert.equal(result, 'foobar');
-  });
-
-  await t.test('handles buffer data', async () => {
-    const stream = new Readable({
-      read() {
-        this.push(Buffer.from('foo'));
-        this.push(Buffer.from('bar'));
-        this.push(null);
-      }
-    });
-    const result = await readStreamAsString(stream);
-    assert.equal(result, 'foobar');
-  });
-});
-
 test('combineStreams', async (t) => {
   await t.test('works with a single stream', async () => {
     const stream = Readable.from(['foo', 'bar']);