diff --git a/tests/lib/cli-engine/cli-engine.js b/tests/lib/cli-engine/cli-engine.js
index b215b0d315b..b4d65fa1163 100644
--- a/tests/lib/cli-engine/cli-engine.js
+++ b/tests/lib/cli-engine/cli-engine.js
@@ -102,7 +102,15 @@ describe("CLIEngine", () => {
     }
 
     // copy into clean area so as not to get "infected" by this project's .eslintrc files
-    before(() => {
+    before(function() {
+
+        /*
+         * GitHub Actions Windows and macOS runners occasionally exhibit
+         * extremely slow filesystem operations, during which copying fixtures
+         * exceeds the default test timeout, so raise it just for this hook.
+         * Mocha uses `this` to set timeouts on an individual hook level.
+         */
+        this.timeout(60 * 1000); // eslint-disable-line no-invalid-this
         shell.mkdir("-p", fixtureDir);
         shell.cp("-r", "./tests/fixtures/.", fixtureDir);
     });
diff --git a/tests/lib/cli-engine/file-enumerator.js b/tests/lib/cli-engine/file-enumerator.js
index 43728862d95..7f91b2a95f4 100644
--- a/tests/lib/cli-engine/file-enumerator.js
+++ b/tests/lib/cli-engine/file-enumerator.js
@@ -211,7 +211,16 @@ describe("FileEnumerator", () => {
                 );
             }
 
-            before(() => {
+            before(function() {
+
+                /*
+                 * GitHub Actions Windows and macOS runners occasionally
+                 * exhibit extremely slow filesystem operations, during which
+                 * copying fixtures exceeds the default test timeout, so raise
+                 * it just for this hook. Mocha uses `this` to set timeouts on
+                 * an individual hook level.
+                 */
+                this.timeout(60 * 1000); // eslint-disable-line no-invalid-this
                 fixtureDir = `${os.tmpdir()}/eslint/tests/fixtures/`;
                 sh.mkdir("-p", fixtureDir);
                 sh.cp("-r", "./tests/fixtures/*", fixtureDir);
diff --git a/tests/lib/cli.js b/tests/lib/cli.js
index a1d9a23e491..0f8a24c2e28 100644
--- a/tests/lib/cli.js
+++ b/tests/lib/cli.js
@@ -82,7 +82,15 @@ describe("cli", () => {
     }
 
     // copy into clean area so as not to get "infected" by this project's .eslintrc files
-    before(() => {
+    before(function() {
+
+        /*
+         * GitHub Actions Windows and macOS runners occasionally exhibit
+         * extremely slow filesystem operations, during which copying fixtures
+         * exceeds the default test timeout, so raise it just for this hook.
+         * Mocha uses `this` to set timeouts on an individual hook level.
+         */
+        this.timeout(60 * 1000); // eslint-disable-line no-invalid-this
         fixtureDir = `${os.tmpdir()}/eslint/fixtures`;
         sh.mkdir("-p", fixtureDir);
         sh.cp("-r", "./tests/fixtures/.", fixtureDir);
diff --git a/tests/lib/eslint/eslint.js b/tests/lib/eslint/eslint.js
index dbb0059286c..d6abf5a8bda 100644
--- a/tests/lib/eslint/eslint.js
+++ b/tests/lib/eslint/eslint.js
@@ -86,7 +86,15 @@ describe("ESLint", () => {
     }
 
     // copy into clean area so as not to get "infected" by this project's .eslintrc files
-    before(() => {
+    before(function() {
+
+        /*
+         * GitHub Actions Windows and macOS runners occasionally exhibit
+         * extremely slow filesystem operations, during which copying fixtures
+         * exceeds the default test timeout, so raise it just for this hook.
+         * Mocha uses `this` to set timeouts on an individual hook level.
+         */
+        this.timeout(60 * 1000); // eslint-disable-line no-invalid-this
         shell.mkdir("-p", fixtureDir);
         shell.cp("-r", "./tests/fixtures/.", fixtureDir);
     });