diff --git a/test/buildPronoun.test.js b/test/buildPronoun.test.js
index 93c0cd979..e32cc5a72 100644
--- a/test/buildPronoun.test.js
+++ b/test/buildPronoun.test.js
@@ -9,69 +9,7 @@ jest.unstable_mockModule('../data/pronouns/morphemes.js', () => {
 
 const { Pronoun } = await import('../src/classes.js');
 const { buildPronoun } = await import('../src/buildPronoun.js');
-
-const pronouns = {
-    he: new Pronoun(
-        'he',
-        'Normative “he/him”',
-        true,
-        {
-            pronoun_subject: 'he',
-            pronoun_object: 'him',
-            possessive_determiner: 'his',
-            possessive_pronoun: 'his',
-            reflexive: 'himself',
-        },
-        [false],
-        [false],
-        ['he/him'],
-        '',
-        true,
-        '',
-        '',
-        '',
-    ),
-    she: new Pronoun(
-        'she',
-        'Normative “she/her”',
-        true,
-        {
-            pronoun_subject: 'she',
-            pronoun_object: 'her',
-            possessive_determiner: 'her',
-            possessive_pronoun: 'hers',
-            reflexive: 'herself',
-        },
-        [false],
-        [false],
-        ['she/her'],
-        '',
-        true,
-        '',
-        '',
-        '',
-    ),
-    they: new Pronoun(
-        'they',
-        'Singular “they”',
-        true,
-        {
-            pronoun_subject: 'they',
-            pronoun_object: 'them',
-            possessive_determiner: 'their',
-            possessive_pronoun: 'theirs',
-            reflexive: 'themselves',
-        },
-        [true],
-        [true],
-        ['they/them'],
-        '',
-        true,
-        '',
-        'themselves',
-        '',
-    ),
-};
+const { default: pronouns } = await import('./fixtures/pronouns.js');
 
 beforeEach(() => {
     global.config.pronouns = {
diff --git a/test/classes.test.js b/test/classes.test.js
new file mode 100644
index 000000000..de1d97af3
--- /dev/null
+++ b/test/classes.test.js
@@ -0,0 +1,61 @@
+import { describe, expect, test } from '@jest/globals';
+
+import { PronounGroup, PronounLibrary } from '../src/classes.js';
+
+import pronouns from './fixtures/pronouns.js';
+
+describe('when merging pronoun groups by key', () => {
+    test('groups without keys are not assigned a merged group', () => {
+        const groups = [
+            new PronounGroup('Normative-ish forms', ['they']),
+        ];
+        const library = new PronounLibrary(groups, pronouns);
+        expect(library.byKey()).toEqual({});
+    });
+
+    test('groups with different keys are assigned different merged groups', () => {
+        const groups = [
+            new PronounGroup('Binary forms', ['he', 'she'], null, 'normative'),
+            new PronounGroup('Normative-ish forms', ['they'], null, 'normative-ish'),
+        ];
+        const library = new PronounLibrary(groups, pronouns);
+        expect(library.byKey()).toEqual(
+            {
+                'normative': [
+                    {
+                        group: groups[0],
+                        groupPronouns: { he: pronouns.he, she: pronouns.she },
+                    },
+                ],
+                'normative-ish': [
+                    {
+                        group: groups[1],
+                        groupPronouns: { they: pronouns.they },
+                    },
+                ],
+            },
+        );
+    });
+
+    test('groups with same key are assigned same merged group', () => {
+        const groups = [
+            new PronounGroup('Binary forms', ['he', 'she'], null, 'normative-ish'),
+            new PronounGroup('Normative-ish forms', ['they'], null, 'normative-ish'),
+        ];
+        const library = new PronounLibrary(groups, pronouns);
+        expect(library.byKey()).toEqual(
+            {
+                'normative-ish': [
+                    {
+                        group: groups[0],
+                        groupPronouns: { he: pronouns.he, she: pronouns.she },
+                    },
+                    {
+                        group: groups[1],
+                        groupPronouns: { they: pronouns.they },
+                    },
+                ],
+            },
+        );
+    });
+});
diff --git a/test/fixtures/pronouns.js b/test/fixtures/pronouns.js
new file mode 100644
index 000000000..e1fbe4665
--- /dev/null
+++ b/test/fixtures/pronouns.js
@@ -0,0 +1,70 @@
+import { Pronoun } from '../../src/classes.js';
+
+const he = new Pronoun(
+    'he',
+    'Normative “he/him”',
+    true,
+    {
+        pronoun_subject: 'he',
+        pronoun_object: 'him',
+        possessive_determiner: 'his',
+        possessive_pronoun: 'his',
+        reflexive: 'himself',
+    },
+    [false],
+    [false],
+    ['he/him'],
+    '',
+    true,
+    '',
+    '',
+    '',
+);
+
+const she = new Pronoun(
+    'she',
+    'Normative “she/her”',
+    true,
+    {
+        pronoun_subject: 'she',
+        pronoun_object: 'her',
+        possessive_determiner: 'her',
+        possessive_pronoun: 'hers',
+        reflexive: 'herself',
+    },
+    [false],
+    [false],
+    ['she/her'],
+    '',
+    true,
+    '',
+    '',
+    '',
+);
+
+const they = new Pronoun(
+    'they',
+    'Singular “they”',
+    true,
+    {
+        pronoun_subject: 'they',
+        pronoun_object: 'them',
+        possessive_determiner: 'their',
+        possessive_pronoun: 'theirs',
+        reflexive: 'themselves',
+    },
+    [true],
+    [true],
+    ['they/them'],
+    '',
+    true,
+    '',
+    'themselves',
+    '',
+);
+
+export default {
+    he,
+    she,
+    they,
+};