In this case, you could want to document how that external API *should* look like. What *path operation* it should have, what body it should expect, what response it should return, etc.

## An app with callbacks { #an-app-with-callbacks }

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

        assertNotNull(writeRequest, "Smb2WriteRequest should implement RequestWithFileId");
        assertNotNull(flushRequest, "Smb2FlushRequest should implement RequestWithFileId");
        assertNotNull(ioctlRequest, "Smb2IoctlRequest should implement RequestWithFileId");
        assertNotNull(lockRequest, "Smb2LockRequest should implement RequestWithFileId");
    }

    @Test
    @DisplayName("Should set file ID correctly in Smb2CloseRequest")

        }

        @Test
        @DisplayName("Should handle null root cause")
        void testConstructorWithNullRootCause() {
            TransportException exception = new TransportException((Throwable) null);

            assertNotNull(exception);
            assertNull(exception.getRootCause());
        }

        @Test
        @DisplayName("Should handle null message with root cause")

            }

            for (int state : connectedStates) {
                transport.setState(state);
                assertFalse(transport.isDisconnected(), "State " + state + " should not be disconnected");
            }
        }

        @Test
        @DisplayName("should correctly identify failed states")

        // Then
        assertNotNull(nonce1, "First secure nonce should not be null");
        assertNotNull(nonce2, "Second secure nonce should not be null");
        assertFalse(Arrays.equals(nonce1, nonce2), "Secure nonces should be different");
        assertTrue(nonce1.length > 0, "Secure nonce should have proper length");
    }

    @Test
    @DisplayName("Should handle concurrent secure nonce generation safely")

        assertNotNull(pairs, "Decoded pairs should not be null");
        assertEquals(1, pairs.size(), "Should have decoded one pair");

        AvPair pair = pairs.get(0);
        assertEquals(unknownType, pair.getType(), "Pair type should match unknown type");
        assertFalse(pair instanceof AvFlags, "Should not be decoded as specific type");
        assertFalse(pair instanceof AvTimestamp, "Should not be decoded as specific type");
    }

                    "Dialect " + String.format("0x%04X", dialect) + " should be >= SMB 2.0.2");
        }

        @Test
        @DisplayName("Dialects should be in ascending order")
        void testDialectOrdering() {
            assertTrue(Smb2Constants.SMB2_DIALECT_0202 < Smb2Constants.SMB2_DIALECT_0210, "SMB 2.0.2 should be less than SMB 2.1");

        assertFalse(file.exists(), "File should not exist initially");

        file.createNewFile();
        assertTrue(file.exists(), "File should exist after creation");
        assertTrue(file.isFile(), "Should be identified as a file");
        assertFalse(file.isDirectory(), "Should not be identified as a directory");
        assertEquals(0, file.length(), "New file should have zero length");
    }

    @Test

    }

    @Test
    @DisplayName("Constructor should initialize TransPeekNamedPipeResponse")
    void testConstructor() {
        // Assert
        assertNotNull(response);
        assertTrue(response instanceof SmbComTransactionResponse);
        assertEquals(0, response.getAvailable());
    }

    @Test
    @DisplayName("Should verify status constants are correctly defined")
    void testStatusConstants() {

            assertEquals(TIME_LOW, uuid.time_low, "time_low should match");
            assertEquals(TIME_MID, uuid.time_mid, "time_mid should match");
            assertEquals(TIME_HI_AND_VERSION, uuid.time_hi_and_version, "time_hi_and_version should match");
            assertEquals(CLOCK_SEQ_HI_AND_RESERVED, uuid.clock_seq_hi_and_reserved, "clock_seq_hi_and_reserved should match");