diff --git a/tests/Unit/StringPluralForm/FiveFormsIrishTest.php b/tests/Unit/StringPluralForm/FiveFormsIrishTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..c22f7edb8f3a983dcb5ab76712979f045d7f35ee
--- /dev/null
+++ b/tests/Unit/StringPluralForm/FiveFormsIrishTest.php
@@ -0,0 +1,73 @@
+<?php
+
+namespace Drupal\Tests\string_plural_form\Unit\StringPluralForm;
+
+use Drupal\string_plural_form\Plugin\StringPluralForm\FiveFormsIrish;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\string_plural_form\Plugin\StringPluralForm\FiveFormsIrish
+ * @group StringPluralFormPlugins
+ */
+class FiveFormsIrishTest extends UnitTestCase {
+
+  /**
+   * Tests \Drupal\string_plural_form\Plugin\StringPluralForm\FiveFormsIrish::getGettextNplurals()
+   */
+  public function testGetGettextNplurals() {
+    $plugin = new FiveFormsIrish();
+    $this->assertEquals(5, $plugin->getGettextNplurals());
+  }
+
+  /**
+   * Tests \Drupal\string_plural_form\Plugin\StringPluralForm\FiveFormsIrish::getGettextNplurals()
+   */
+  public function testGetGettextPlural() {
+    $plugin = new FiveFormsIrish();
+    $this->assertEquals("(n==1 ? 0 : n==2 ? 1 : n>=3 && n<=6 ? 2 : n>=7 && n<=10 ? 3 : 4)", $plugin->getGettextPlural());
+  }
+
+  /**
+   * Tests \Drupal\string_plural_form\Plugin\StringPluralForm\FiveFormsIrish::getIndex()
+   */
+  public function testGetIndex() {
+
+    $plugin = new FiveFormsIrish();
+
+    $expected_forms = [
+      0 => [1],
+      1 => [2],
+      2 => [3, 4, 5, 6],
+      3 => [7, 8, 9, 10],
+      4 => [
+        0,
+        11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
+        21, 22, 23, 24, 25, 26, 27, 28, 29, 30,
+        31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
+        41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
+        51, 52, 53, 54, 55, 56, 57, 58, 59, 60,
+        61, 62, 63, 64, 65, 66, 67, 68, 69, 70,
+        71, 72, 73, 74, 75, 76, 77, 78, 79, 80,
+        81, 82, 83, 84, 85, 86, 87, 88, 89, 90,
+        91, 92, 93, 94, 95, 96, 97, 98, 99, 100,
+        101, 102, 103, 104, 105, 106, 107, 108, 109, 110,
+        111, 112, 113, 114, 115, 116, 117, 118, 119, 120,
+        121, 122, 123, 124, 125, 126, 127, 128, 129, 130,
+        131, 132, 133, 134, 135, 136, 137, 138, 139, 140,
+        141, 142, 143, 144, 145, 146, 147, 148, 149, 150,
+        151, 152, 153, 154, 155, 156, 157, 158, 159, 160,
+        161, 162, 163, 164, 165, 166, 167, 168, 169, 170,
+        171, 172, 173, 174, 175, 176, 177, 178, 179, 180,
+        181, 182, 183, 184, 185, 186, 187, 188, 189, 190,
+        191, 192, 193, 194, 195, 196, 197, 198, 199,
+      ],
+    ];
+
+    foreach ($expected_forms as $index => $numbers) {
+      foreach ($numbers as $n) {
+        $this->assertEquals($index, $plugin->getIndex($n));
+      }
+    }
+  }
+
+}