test: improve coverage of fs internal utils

Refs: https://coverage.nodejs.org/coverage-910efc2d9a69ac32/lib/internal/fs/utils.js.html#L634

PR-URL: #38746
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-fs-util-validateoffsetlength.js

@@ -0,0 +1,87 @@
+// Flags: --expose-internals
+'use strict';
+
+const common = require('../common');
+
+const assert = require('assert');
+const {
+  validateOffsetLengthRead,
+  validateOffsetLengthWrite,
+} = require('internal/fs/utils');
+
+{
+  const offset = -1;
+  assert.throws(
+    () => validateOffsetLengthRead(offset, 0, 0),
+    common.expectsError({
+      code: 'ERR_OUT_OF_RANGE',
+      name: 'RangeError',
+      message: 'The value of "offset" is out of range. ' +
+                 `It must be >= 0. Received ${offset}`
+    })
+  );
+}
+
+{
+  const length = -1;
+  assert.throws(
+    () => validateOffsetLengthRead(0, length, 0),
+    common.expectsError({
+      code: 'ERR_OUT_OF_RANGE',
+      name: 'RangeError',
+      message: 'The value of "length" is out of range. ' +
+                 `It must be >= 0. Received ${length}`
+    })
+  );
+}
+
+{
+  const offset = 1;
+  const length = 1;
+  const byteLength = offset + length - 1;
+  assert.throws(
+    () => validateOffsetLengthRead(offset, length, byteLength),
+    common.expectsError({
+      code: 'ERR_OUT_OF_RANGE',
+      name: 'RangeError',
+      message: 'The value of "length" is out of range. ' +
+                 `It must be <= ${byteLength - offset}. Received ${length}`
+    })
+  );
+}
+
+// Most platforms don't allow reads or writes >= 2 GB.
+// See https://github.com/libuv/libuv/pull/1501.
+const kIoMaxLength = 2 ** 31 - 1;
+
+// RangeError when offset > byteLength
+{
+  const offset = 100;
+  const length = 100;
+  const byteLength = 50;
+  assert.throws(
+    () => validateOffsetLengthWrite(offset, length, byteLength),
+    common.expectsError({
+      code: 'ERR_OUT_OF_RANGE',
+      name: 'RangeError',
+      message: 'The value of "offset" is out of range. ' +
+               `It must be <= ${byteLength}. Received ${offset}`
+    })
+  );
+}
+
+// RangeError when byteLength < kIoMaxLength, and length > byteLength - offset.
+{
+  const offset = kIoMaxLength - 150;
+  const length = 200;
+  const byteLength = kIoMaxLength - 100;
+  assert.throws(
+    () => validateOffsetLengthWrite(offset, length, byteLength),
+    common.expectsError({
+      code: 'ERR_OUT_OF_RANGE',
+      name: 'RangeError',
+      message: 'The value of "length" is out of range. ' +
+               `It must be <= ${byteLength - offset}. Received ${length}`
+    })
+  );
+}