ExtendedSmbTree middle = smbTree.unwrap(ExtendedSmbTree.class);
        CustomSmbTree inner = middle.unwrap(CustomSmbTree.class);

        assertNotNull(middle, "Middle tree should not be null");
        assertNotNull(inner, "Inner tree should not be null");
        assertSame(middleTree, middle, "Should return correct middle tree");

    void testJoinWithEmptyStringElements() {
        String result = StringUtil.join(",", "", "middle", "");
        // First element is empty string (sb becomes "")
        // Second: sb.length() is 0, no delimiter, append "middle" (sb becomes "middle")
        // Third: sb.length() > 0, add delimiter + "" (sb becomes "middle,")
        assertEquals("middle,", result);
    }

    @Test

        // Test constructor with nested exception causes
        Exception rootCause = new IllegalStateException("Root cause");
        Exception middleCause = new RuntimeException("Middle cause", rootCause);
        String message = "Top level dictionary error";
        DictionaryException exception = new DictionaryException(message, middleCause);

        assertNotNull(exception);

        Throwable middleCause = new IllegalStateException("Middle cause", rootCause);
        ScheduledJobException exception = new ScheduledJobException("Top level error", middleCause);

        assertEquals("Top level error", exception.getMessage());
        assertEquals(middleCause, exception.getCause());
        assertEquals("Middle cause", exception.getCause().getMessage());

        void testToStringWithNestedExceptions() {
            Exception innermost = new IOException("Innermost exception");
            Exception middle = new RuntimeException("Middle exception", innermost);
            Exception rootCause = new IllegalStateException("Outer exception", middle);
            TransportException exception = new TransportException("Transport failed", rootCause);

            String result = exception.toString();

                Arguments.of(makeSeq(8), 0, 8, 0), // full copy at index 0
                Arguments.of(makeSeq(10), 2, 5, 3), // middle slice, non-zero dst index
                Arguments.of(makeSeq(4), 4, 0, 0), // zero-length slice at end
                Arguments.of(makeSeq(16), 7, 3, 0), // small slice from middle
                Arguments.of(makeSeq(16), 0, 0, 5) // zero-length with non-zero dst index
        );
    }

    }

    /**
     * Test getMessageByDcerpcError() with a known error code (middle element).
     */
    @Test
    void testGetMessageByDcerpcError_middleElement() {
        String message = DcerpcException.getMessageByDcerpcError(DcerpcError.DCERPC_FAULT_INVALID_TAG);
        assertEquals("DCERPC_FAULT_INVALID_TAG", message, "Should return correct message for middle element.");
    }

    /**

        // Test constructor with nested exception causes
        Throwable rootCause = new IllegalArgumentException("Root cause");
        Throwable middleCause = new IllegalStateException("Middle cause", rootCause);
        String message = "Command execution failed with nested exception";

        CommandExecutionException exception = new CommandExecutionException(message, middleCause);

<img src="/img/tutorial/extending-openapi/image03.png">

## Change the Theme { #change-the-theme }

The same way you could set the syntax highlighting theme with the key `"syntaxHighlight.theme"` (notice that it has a dot in the middle):

{* ../../docs_src/configure_swagger_ui/tutorial002.py hl[3] *}

That configuration would change the syntax highlighting color theme:

<img src="/img/tutorial/extending-openapi/image04.png">

///

So, you should be able to pin to a version like:

```txt
fastapi>=0.45.0,<0.46.0
```

Breaking changes and new features are added in "MINOR" versions.

/// tip

The "MINOR" is the number in the middle, for example, in `0.2.3`, the MINOR version is `2`.

///

## Upgrading the FastAPI versions { #upgrading-the-fastapi-versions }

You should add tests for your app.