diff --git a/packages/rstack/rstack.config.ts b/packages/rstack/rstack.config.ts
index d7777d8..789bc1f 100644
--- a/packages/rstack/rstack.config.ts
+++ b/packages/rstack/rstack.config.ts
@@ -7,6 +7,8 @@ define.test(async () => {
   process.env.NO_COLOR = '1';
 
   return {
+    // Temporary projects may contain files that match Rstest's test glob.
+    exclude: ['**/test-temp-*/**'],
     extends: withRslibConfig(),
     source: {
       tsconfigPath: './tests/tsconfig.json',
diff --git a/packages/rstack/tests/cli/fmt/index.test.ts b/packages/rstack/tests/cli/fmt/index.test.ts
index 6312782..283773f 100644
--- a/packages/rstack/tests/cli/fmt/index.test.ts
+++ b/packages/rstack/tests/cli/fmt/index.test.ts
@@ -6,11 +6,10 @@ import { RSTACK_BIN_PATH } from '#test-helpers';
 
 let projectPath: string;
 
-const writeProjectFile = (filePath: string, content: string): string => {
+const writeProjectFile = (filePath: string, content: string): void => {
   const absolutePath = path.join(projectPath, filePath);
   mkdirSync(path.dirname(absolutePath), { recursive: true });
   writeFileSync(absolutePath, content);
-  return absolutePath;
 };
 
 const readProjectFile = (filePath: string): string =>
@@ -30,7 +29,9 @@ const runCLI = (args: string[]) => {
 const runFmt = (args: string[] = []) => runCLI(['fmt', ...args]);
 
 beforeEach(() => {
-  projectPath = mkdtempSync(path.join(import.meta.dirname, 'fmt-project-'));
+  projectPath = mkdtempSync(path.join(import.meta.dirname, 'test-temp-fmt-'));
+  // Prevent repository-level ignore rules from affecting the fixture.
+  mkdirSync(path.join(projectPath, '.git'));
   writeProjectFile('rstack.config.ts', 'export {};\n');
 });
 
diff --git a/packages/rstack/tests/cli/setup/index.test.ts b/packages/rstack/tests/cli/setup/index.test.ts
index 2429e69..da7c13a 100644
--- a/packages/rstack/tests/cli/setup/index.test.ts
+++ b/packages/rstack/tests/cli/setup/index.test.ts
@@ -1,6 +1,5 @@
 import { spawnSync } from 'node:child_process';
 import { existsSync, mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
-import { tmpdir } from 'node:os';
 import path from 'node:path';
 import { afterEach, beforeEach } from 'rstack/test';
 import { RSTACK_BIN_PATH, test } from '#test-helpers';
@@ -30,9 +29,11 @@ const runSetup = (args: string[], runCwd: string = cwd) =>
   });
 
 beforeEach(() => {
-  cwd = mkdtempSync(path.join(tmpdir(), 'rstack setup '));
+  cwd = mkdtempSync(path.join(import.meta.dirname, 'test-temp-rstack setup '));
   env = {
     ...process.env,
+    // Keep Git from treating the fixture as part of this repository.
+    GIT_CEILING_DIRECTORIES: import.meta.dirname,
     GIT_CONFIG_GLOBAL: path.join(cwd, 'global.gitconfig'),
     GIT_CONFIG_NOSYSTEM: '1',
   };
@@ -106,7 +107,9 @@ test('installs a custom hooks directory from a nested project', ({ execCli, expe
 });
 
 test('skips non-Git directories without creating files', ({ execCli, expect }) => {
-  expect(execCli('setup', { cwd })).toContain('Git hooks setup skipped: not a Git repository.');
+  expect(execCli('setup', { cwd, env })).toContain(
+    'Git hooks setup skipped: not a Git repository.',
+  );
   expect(existsSync(path.join(cwd, '.rstack'))).toBe(false);
 });
 
diff --git a/packages/rstack/tests/cli/staged/fmt.test.ts b/packages/rstack/tests/cli/staged/fmt.test.ts
index 1ce8fa1..e9c4829 100644
--- a/packages/rstack/tests/cli/staged/fmt.test.ts
+++ b/packages/rstack/tests/cli/staged/fmt.test.ts
@@ -35,7 +35,7 @@ const runStaged = () =>
   });
 
 beforeEach(() => {
-  projectPath = mkdtempSync(path.join(import.meta.dirname, 'staged-fmt-project-'));
+  projectPath = mkdtempSync(path.join(import.meta.dirname, 'test-temp-staged-fmt-'));
   env = {
     ...process.env,
     GIT_CONFIG_GLOBAL: path.join(projectPath, 'global.gitconfig'),
diff --git a/packages/rstack/tests/config/reload-app-config/index.test.ts b/packages/rstack/tests/config/reload-app-config/index.test.ts
index d4bcfb3..cdf6206 100644
--- a/packages/rstack/tests/config/reload-app-config/index.test.ts
+++ b/packages/rstack/tests/config/reload-app-config/index.test.ts
@@ -1,4 +1,4 @@
-import { rm, writeFile } from 'node:fs/promises';
+import { writeFile } from 'node:fs/promises';
 import path from 'node:path';
 import { getRandomPort, waitForFile } from '@rstackjs/test-utils';
 import { test } from '#test-helpers';
@@ -11,8 +11,6 @@ test('should restart dev server and reload config when Rstack config changes', a
   const dist2 = await prepareDist('dist-2');
   const configFile = path.join(import.meta.dirname, 'test-temp-rstack.config.ts');
 
-  await rm(configFile, { force: true });
-
   await writeFile(
     configFile,
     `import { define } from 'rstack';
diff --git a/packages/rstack/tests/exports/lint-subpath/index.test.ts b/packages/rstack/tests/exports/lint-subpath/index.test.ts
index 75061e7..90136f1 100644
--- a/packages/rstack/tests/exports/lint-subpath/index.test.ts
+++ b/packages/rstack/tests/exports/lint-subpath/index.test.ts
@@ -7,6 +7,5 @@ test('should expose lint APIs from `rstack/lint`', async () => {
 
   for (const method of commonLintMethods) {
     expect(lint).toHaveProperty(method);
-    expect(typeof lint[method]).toBeTruthy();
   }
 });
diff --git a/packages/rstack/tests/exports/test-subpath/index.test.ts b/packages/rstack/tests/exports/test-subpath/index.test.ts
index 191be88..74d693a 100644
--- a/packages/rstack/tests/exports/test-subpath/index.test.ts
+++ b/packages/rstack/tests/exports/test-subpath/index.test.ts
@@ -7,6 +7,5 @@ test('should expose test APIs from `rstack/test`', async () => {
 
   for (const method of commonTestMethods) {
     expect(test).toHaveProperty(method);
-    expect(typeof test[method]).toBeTruthy();
   }
 });
diff --git a/packages/rstack/tests/fmt/discoverPaths.test.ts b/packages/rstack/tests/fmt/discoverPaths.test.ts
index 64f2add..7de16a3 100644
--- a/packages/rstack/tests/fmt/discoverPaths.test.ts
+++ b/packages/rstack/tests/fmt/discoverPaths.test.ts
@@ -1,31 +1,14 @@
-import { mkdirSync, mkdtempSync, rmSync, symlinkSync, writeFileSync } from 'node:fs';
-import { tmpdir } from 'node:os';
+import { symlinkSync } from 'node:fs';
 import path from 'node:path';
 import { expect, test } from 'rstack/test';
 import { discoverFmtPaths } from '../../src/fmt/discoverPaths.ts';
-
-const withProject = async (callback: (rootPath: string) => Promise<void>): Promise<void> => {
-  const rootPath = mkdtempSync(path.join(tmpdir(), 'rstack fmt '));
-
-  try {
-    await callback(rootPath);
-  } finally {
-    rmSync(rootPath, { force: true, recursive: true });
-  }
-};
-
-const writeProjectFile = (rootPath: string, filePath: string, content = ''): string => {
-  const absolutePath = path.join(rootPath, filePath);
-  mkdirSync(path.dirname(absolutePath), { recursive: true });
-  writeFileSync(absolutePath, content);
-  return absolutePath;
-};
+import { withTempProject, writeProjectFile } from './helpers.ts';
 
 const relativePaths = (rootPath: string, files: string[]): string[] =>
   files.map((filePath) => path.relative(rootPath, filePath));
 
 test('discovers non-binary files in stable order and skips hard-ignored paths', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     writeProjectFile(rootPath, 'b.ts');
     writeProjectFile(rootPath, 'a.js');
     writeProjectFile(rootPath, 'folder with spaces/c.ts');
@@ -50,7 +33,7 @@ test('discovers non-binary files in stable order and skips hard-ignored paths',
 });
 
 test('combines files, directories, and globs without duplicates', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     const firstFilePath = writeProjectFile(rootPath, 'src/a.ts');
     writeProjectFile(rootPath, 'src/b.js');
     writeProjectFile(rootPath, 'test/c.ts');
@@ -90,8 +73,7 @@ test('combines files, directories, and globs without duplicates', async () => {
 });
 
 test('applies nested gitignore rules with child negation', async () => {
-  await withProject(async (rootPath) => {
-    mkdirSync(path.join(rootPath, '.git'));
+  await withTempProject(async (rootPath) => {
     writeProjectFile(rootPath, '.gitignore', '*.js\ndist/\n');
     writeProjectFile(rootPath, 'src/.gitignore', '!keep.js\n');
     writeProjectFile(rootPath, 'dist/.gitignore', '!keep.js\n');
@@ -114,8 +96,7 @@ test('applies nested gitignore rules with child negation', async () => {
 });
 
 test('lets explicit files bypass gitignore', async () => {
-  await withProject(async (rootPath) => {
-    mkdirSync(path.join(rootPath, '.git'));
+  await withTempProject(async (rootPath) => {
     writeProjectFile(rootPath, '.gitignore', '/generated/\n');
     const keepPath = writeProjectFile(rootPath, 'generated/keep.ts');
     writeProjectFile(rootPath, 'src/index.ts');
@@ -132,7 +113,7 @@ test('lets explicit files bypass gitignore', async () => {
 });
 
 test.runIf(process.platform !== 'win32')('does not follow file or directory symlinks', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     const targetPath = writeProjectFile(rootPath, 'target/index.ts');
     symlinkSync(path.join(rootPath, 'target'), path.join(rootPath, 'linked-directory'));
     symlinkSync(targetPath, path.join(rootPath, 'linked-file.ts'));
diff --git a/packages/rstack/tests/fmt/discovery.test.ts b/packages/rstack/tests/fmt/discovery.test.ts
index 4b8e866..e90fb40 100644
--- a/packages/rstack/tests/fmt/discovery.test.ts
+++ b/packages/rstack/tests/fmt/discovery.test.ts
@@ -1,27 +1,10 @@
-import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
-import { tmpdir } from 'node:os';
+import { mkdirSync } from 'node:fs';
 import path from 'node:path';
 import { expect, test } from 'rstack/test';
 import { normalizeFmtConfig } from '../../src/fmt/config.ts';
 import { discoverFmtFiles } from '../../src/fmt/discovery.ts';
 import type { FmtConfig } from '../../src/fmt/types.ts';
-
-const withProject = async (callback: (rootPath: string) => Promise<void>): Promise<void> => {
-  const rootPath = mkdtempSync(path.join(tmpdir(), 'rstack fmt '));
-
-  try {
-    await callback(rootPath);
-  } finally {
-    rmSync(rootPath, { force: true, recursive: true });
-  }
-};
-
-const writeProjectFile = (rootPath: string, filePath: string, content = ''): string => {
-  const absolutePath = path.join(rootPath, filePath);
-  mkdirSync(path.dirname(absolutePath), { recursive: true });
-  writeFileSync(absolutePath, content);
-  return absolutePath;
-};
+import { withTempProject, writeProjectFile } from './helpers.ts';
 
 const discover = async (cwd: string, patterns?: string[], config?: FmtConfig, configRoot = cwd) =>
   discoverFmtFiles({
@@ -34,7 +17,7 @@ const relativePaths = (rootPath: string, files: Awaited<ReturnType<typeof discov
   files.map((file) => path.relative(rootPath, file.path));
 
 test('applies config ignore patterns to discovered and explicit files', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     const keepPath = writeProjectFile(rootPath, 'generated/keep.ts');
     const blockedPath = writeProjectFile(rootPath, 'generated/blocked.ts');
     writeProjectFile(rootPath, 'src/index.ts');
@@ -52,7 +35,7 @@ test('applies config ignore patterns to discovered and explicit files', async ()
 });
 
 test('applies config ignore patterns outside the config root', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     const configRoot = path.join(rootPath, 'project');
     const filePath = writeProjectFile(rootPath, 'shared/index.ts');
     mkdirSync(configRoot);
@@ -64,7 +47,7 @@ test('applies config ignore patterns outside the config root', async () => {
 });
 
 test('resolves parsers and accepts unknown extensions with an explicit parser', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     writeProjectFile(rootPath, 'index.ts');
     writeProjectFile(rootPath, 'source.custom');
     writeProjectFile(rootPath, 'unknown.extension');
diff --git a/packages/rstack/tests/fmt/helpers.ts b/packages/rstack/tests/fmt/helpers.ts
new file mode 100644
index 0000000..89d280c
--- /dev/null
+++ b/packages/rstack/tests/fmt/helpers.ts
@@ -0,0 +1,23 @@
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import path from 'node:path';
+
+export const withTempProject = async (
+  callback: (rootPath: string) => Promise<void>,
+): Promise<void> => {
+  const rootPath = mkdtempSync(path.join(import.meta.dirname, 'test-temp-fmt-'));
+  // Prevent repository-level ignore rules from affecting the fixture.
+  mkdirSync(path.join(rootPath, '.git'));
+
+  try {
+    await callback(rootPath);
+  } finally {
+    rmSync(rootPath, { force: true, recursive: true });
+  }
+};
+
+export const writeProjectFile = (rootPath: string, filePath: string, content = ''): string => {
+  const absolutePath = path.join(rootPath, filePath);
+  mkdirSync(path.dirname(absolutePath), { recursive: true });
+  writeFileSync(absolutePath, content);
+  return absolutePath;
+};
diff --git a/packages/rstack/tests/fmt/runner.test.ts b/packages/rstack/tests/fmt/runner.test.ts
index f789e21..07377e8 100644
--- a/packages/rstack/tests/fmt/runner.test.ts
+++ b/packages/rstack/tests/fmt/runner.test.ts
@@ -1,27 +1,9 @@
-import {
-  chmodSync,
-  mkdtempSync,
-  readFileSync,
-  rmSync,
-  statSync,
-  utimesSync,
-  writeFileSync,
-} from 'node:fs';
-import { tmpdir } from 'node:os';
+import { chmodSync, readFileSync, statSync, utimesSync, writeFileSync } from 'node:fs';
 import path from 'node:path';
 import { expect, test } from 'rstack/test';
 import { runFmtFiles } from '../../src/fmt/runner.ts';
 import type { FmtFileRequest, FmtMode } from '../../src/fmt/types.ts';
-
-const withProject = async (callback: (rootPath: string) => Promise<void>): Promise<void> => {
-  const rootPath = mkdtempSync(path.join(tmpdir(), 'rstack fmt runner '));
-
-  try {
-    await callback(rootPath);
-  } finally {
-    rmSync(rootPath, { force: true, recursive: true });
-  }
-};
+import { withTempProject } from './helpers.ts';
 
 const createRequest = (filePath: string): FmtFileRequest => ({
   path: filePath,
@@ -40,7 +22,7 @@ const run = (files: FmtFileRequest[], mode: FmtMode = 'write') =>
   });
 
 test('does not rewrite unchanged files', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     const filePath = path.join(rootPath, 'unchanged.ts');
     const timestamp = new Date('2020-01-01T00:00:00.000Z');
     writeFileSync(filePath, 'const value = 1;\n');
@@ -60,7 +42,7 @@ test('does not rewrite unchanged files', async () => {
 });
 
 test('writes changed files', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     const filePath = path.join(rootPath, 'changed.ts');
     writeFileSync(filePath, 'const value=1');
 
@@ -75,7 +57,7 @@ test('writes changed files', async () => {
 });
 
 test.runIf(process.platform !== 'win32')('preserves file mode when writing', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     const filePath = path.join(rootPath, 'executable.ts');
     writeFileSync(filePath, 'const value=1');
     chmodSync(filePath, 0o744);
@@ -88,7 +70,7 @@ test.runIf(process.platform !== 'win32')('preserves file mode when writing', asy
 
 for (const mode of ['check', 'list-different'] as const) {
   test(`${mode} reports differences without writing`, async () => {
-    await withProject(async (rootPath) => {
+    await withTempProject(async (rootPath) => {
       const filePath = path.join(rootPath, 'different.ts');
       const source = 'const value=1';
       writeFileSync(filePath, source);
@@ -105,7 +87,7 @@ for (const mode of ['check', 'list-different'] as const) {
 }
 
 test('continues after a file fails and gives errors exit-code precedence', async () => {
-  await withProject(async (rootPath) => {
+  await withTempProject(async (rootPath) => {
     const invalidPath = path.join(rootPath, 'invalid.ts');
     const validPath = path.join(rootPath, 'valid.ts');
     writeFileSync(invalidPath, 'const value = ;');
diff --git a/packages/rstack/tests/helpers/cliTest.ts b/packages/rstack/tests/helpers/cliTest.ts
index cb583d4..f3ff322 100644
--- a/packages/rstack/tests/helpers/cliTest.ts
+++ b/packages/rstack/tests/helpers/cliTest.ts
@@ -26,11 +26,10 @@ export type CliTestFixtures = {
 type CliTest = ReturnType<typeof baseTest.extend<CliTestFixtures>>;
 
 function makeBox(title: string) {
-  const header = `-------- Logs from: "${title}" --------`;
-  const footer = `-------- Logs from: "${title}" --------`;
+  const border = `-------- Logs from: "${title}" --------`;
   return {
-    header: `\n${header}\n`,
-    footer: `${footer}\n`,
+    header: `\n${border}\n`,
+    footer: `${border}\n`,
   };
 }
 
@@ -114,9 +113,8 @@ export const test: CliTest = baseTest.extend<CliTestFixtures>({
     }
   },
   execCliAsync: async ({ exec }, use) => {
-    const execCliAsync: Exec = (command, options = {}) => {
-      return exec(`node "${RSTACK_BIN_PATH}" ${command}`, options);
-    };
+    const execCliAsync: Exec = (command, options = {}) =>
+      exec(`node "${RSTACK_BIN_PATH}" ${command}`, options);
     await use(execCliAsync);
   },
 });
diff --git a/packages/rstack/tests/setup/helpers.ts b/packages/rstack/tests/setup/helpers.ts
index 141df8e..533cb08 100644
--- a/packages/rstack/tests/setup/helpers.ts
+++ b/packages/rstack/tests/setup/helpers.ts
@@ -1,6 +1,5 @@
 import { type SpawnSyncReturns, spawnSync } from 'node:child_process';
 import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
-import { tmpdir } from 'node:os';
 import path from 'node:path';
 
 const hooksDir = '.rstack/hooks';
@@ -22,10 +21,15 @@ export const runGit = (cwd: string, args: string[]): string => {
 };
 
 export const withDirectory = (callback: (cwd: string) => void): void => {
-  const cwd = mkdtempSync(path.join(tmpdir(), 'rstack hooks '));
+  const cwd = mkdtempSync(path.join(import.meta.dirname, 'test-temp-rstack hooks '));
+  const gitCeilingDirectories = process.env.GIT_CEILING_DIRECTORIES;
+  // Keep Git from treating the temporary directory as part of this repository.
+  process.env.GIT_CEILING_DIRECTORIES = import.meta.dirname;
+
   try {
     callback(cwd);
   } finally {
+    restoreEnv('GIT_CEILING_DIRECTORIES', gitCeilingDirectories);
     rmSync(cwd, { force: true, recursive: true });
   }
 };
diff --git a/packages/rstack/tests/setup/hooks.test.ts b/packages/rstack/tests/setup/hooks.test.ts
index ab11a43..9c81021 100644
--- a/packages/rstack/tests/setup/hooks.test.ts
+++ b/packages/rstack/tests/setup/hooks.test.ts
@@ -1,9 +1,9 @@
 import { spawnSync } from 'node:child_process';
-import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from 'node:fs';
-import { tmpdir } from 'node:os';
+import { mkdirSync, writeFileSync } from 'node:fs';
 import path from 'node:path';
 import { expect, test } from 'rstack/test';
 import { createHookFiles } from '../../src/setup/hooks.ts';
+import { withDirectory } from './helpers.ts';
 
 test('generates the dispatcher and all client-side Git hook shims', () => {
   const { runner, ...shims } = createHookFiles();
@@ -29,18 +29,17 @@ test('generates the dispatcher and all client-side Git hook shims', () => {
 });
 
 test.runIf(process.platform !== 'win32')('runs generated hooks', () => {
-  const directory = mkdtempSync(path.join(tmpdir(), 'rstack hooks '));
-  const hooksDirectory = path.join(directory, 'hooks with spaces');
-  const generatedDirectory = path.join(hooksDirectory, '_');
-  const generatedHook = path.join(generatedDirectory, 'pre-commit');
-  const userHook = path.join(hooksDirectory, 'pre-commit');
-  const files = createHookFiles();
-  const env: NodeJS.ProcessEnv = {
-    ...process.env,
-    XDG_CONFIG_HOME: path.join(directory, 'config'),
-  };
+  withDirectory((directory) => {
+    const hooksDirectory = path.join(directory, 'hooks with spaces');
+    const generatedDirectory = path.join(hooksDirectory, '_');
+    const generatedHook = path.join(generatedDirectory, 'pre-commit');
+    const userHook = path.join(hooksDirectory, 'pre-commit');
+    const files = createHookFiles();
+    const env: NodeJS.ProcessEnv = {
+      ...process.env,
+      XDG_CONFIG_HOME: path.join(directory, 'config'),
+    };
 
-  try {
     mkdirSync(generatedDirectory, { recursive: true });
     writeFileSync(path.join(generatedDirectory, 'runner'), files.runner);
     writeFileSync(generatedHook, files['pre-commit']);
@@ -72,7 +71,5 @@ printf 'unreachable\\n'
 
     expect(errexitResult.status).toBe(1);
     expect(errexitResult.stdout).toBe('Rstack - pre-commit hook failed (code 1)\n');
-  } finally {
-    rmSync(directory, { force: true, recursive: true });
-  }
+  });
 });