diff --git a/shell/composables/focusTrap.test.ts b/shell/composables/focusTrap.test.ts
new file mode 100644
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+++ b/shell/composables/focusTrap.test.ts
@@ -0,0 +1,110 @@
+import { getFirstFocusableElement } from './focusTrap';
+
+describe('getFirstFocusableElement', () => {
+  it('returns document.body when the container has no focusable elements', () => {
+    const container = document.createElement('div');
+
+    container.innerHTML = '<span>plain text</span><p>paragraph</p>';
+
+    expect(getFirstFocusableElement(container)).toStrictEqual(document.body);
+  });
+
+  it('returns document.body when no element argument is provided and document has no focusable elements', () => {
+    expect(getFirstFocusableElement()).toStrictEqual(document.body);
+  });
+
+  it.each([
+    {
+      desc: 'button',
+      html: '<button>click me</button>',
+    },
+    {
+      desc: 'anchor',
+      html: '<a href="#">link</a>',
+    },
+    {
+      desc: 'input',
+      html: '<input type="text">',
+    },
+    {
+      desc: 'textarea',
+      html: '<textarea></textarea>',
+    },
+    {
+      desc: 'select',
+      html: '<select><option>opt</option></select>',
+    },
+    {
+      desc: 'details',
+      html: '<details><summary>summary</summary></details>',
+    },
+    {
+      desc: 'element with tabindex="0"',
+      html: '<div tabindex="0">div</div>',
+    },
+    {
+      desc: 'element with tabindex="1"',
+      html: '<div tabindex="1">div</div>',
+    },
+  ])('returns the $desc element when it is the only focusable element', ({ html }) => {
+    const container = document.createElement('div');
+
+    container.innerHTML = html;
+
+    const expected = container.firstElementChild;
+
+    expect(getFirstFocusableElement(container)).toStrictEqual(expected);
+  });
+
+  it('skips a disabled button and returns the next non-disabled focusable element', () => {
+    const container = document.createElement('div');
+
+    container.innerHTML = '<button disabled>disabled</button><button>enabled</button>';
+    const buttons = container.querySelectorAll('button');
+
+    expect(getFirstFocusableElement(container)).toStrictEqual(buttons[1]);
+  });
+
+  it('skips a disabled input and returns the next non-disabled focusable element', () => {
+    const container = document.createElement('div');
+
+    container.innerHTML = '<input disabled type="text"><button>submit</button>';
+    const button = container.querySelector('button');
+
+    expect(getFirstFocusableElement(container)).toStrictEqual(button);
+  });
+
+  it('returns document.body when every focusable element is disabled', () => {
+    const container = document.createElement('div');
+
+    container.innerHTML = '<button disabled>a</button><input disabled type="text"><select disabled><option>x</option></select>';
+
+    expect(getFirstFocusableElement(container)).toStrictEqual(document.body);
+  });
+
+  it('does not return an element with tabindex="-1"', () => {
+    const container = document.createElement('div');
+
+    container.innerHTML = '<div tabindex="-1">not focusable</div>';
+
+    expect(getFirstFocusableElement(container)).toStrictEqual(document.body);
+  });
+
+  it('returns the first of multiple focusable elements', () => {
+    const container = document.createElement('div');
+
+    container.innerHTML = '<button>first</button><button>second</button><input type="text">';
+    const [first] = container.querySelectorAll('button');
+
+    expect(getFirstFocusableElement(container)).toStrictEqual(first);
+  });
+
+  it('returns the first non-disabled element when leading elements are all disabled', () => {
+    const container = document.createElement('div');
+
+    container.innerHTML = '<button disabled>one</button><button disabled>two</button><button>three</button>';
+    const buttons = container.querySelectorAll('button');
+
+    expect(getFirstFocusableElement(container)).toStrictEqual(buttons[2]);
+  });
+});