diff --git a/packages/pi/bunfig.toml b/packages/pi/bunfig.toml
new file mode 100644
index 00000000..1c8dc619
--- /dev/null
+++ b/packages/pi/bunfig.toml
@@ -0,0 +1,2 @@
+[test]
+preload = ["./src/tests/setup.ts"]
diff --git a/packages/pi/src/tests/setup.ts b/packages/pi/src/tests/setup.ts
new file mode 100644
index 00000000..4b03eec9
--- /dev/null
+++ b/packages/pi/src/tests/setup.ts
@@ -0,0 +1,35 @@
+import { afterEach, beforeEach } from 'bun:test'
+import { mkdtemp, rm } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+
+let testDir: string | undefined
+const HOST_PATH_ENV_VARS = [
+  'OPENCODE_CONFIG_DIR',
+  'OPENCODE_ANTHROPIC_AUTH_FILE',
+  'OPENCODE_ANTHROPIC_AUTH_STATE_FILE',
+  'PI_AGENT_DIR',
+  'PI_ANTHROPIC_AUTH_FILE',
+  'PI_ANTHROPIC_AUTH_ROUTING_STATE_FILE',
+  'PI_ANTHROPIC_AUTH_CACHEKEEP_REGISTRY_DIR',
+] as const
+
+beforeEach(async () => {
+  testDir = await mkdtemp(join(tmpdir(), 'anthropic-auth-pi-test-'))
+  for (const key of HOST_PATH_ENV_VARS) delete process.env[key]
+  process.env.OPENCODE_CONFIG_DIR = join(testDir, 'opencode')
+  process.env.OPENCODE_ANTHROPIC_AUTH_FILE = join(
+    testDir,
+    'anthropic-auth.json',
+  )
+  process.env.OPENCODE_ANTHROPIC_AUTH_STATE_FILE = join(
+    testDir,
+    'anthropic-auth-state.json',
+  )
+  process.env.PI_AGENT_DIR = join(testDir, '.pi-agent')
+})
+
+afterEach(async () => {
+  if (testDir) await rm(testDir, { recursive: true, force: true })
+  testDir = undefined
+})