We know the ins and outs of PCB's

• Power supply voltage levels (VCC, VDD, etc.).

• Clock signals (system clock, peripheral clocks).

• Analog input signals (e.g., sensor inputs).

• Digital control signals (e.g., reset, enable signals).

• Serial communication inputs (UART, SPI, I2C).

• External trigger inputs.

• User interface inputs (buttons, switches).

• PWM (Pulse Width Modulation) signals.

• Temperature sensor inputs.

• Voltage reference inputs.

• Digital output signals (data lines, control lines).

• Analog input signals (ADC inputs).

• Analog output signals (DAC outputs).

• LED indicators.

• Display outputs (LCD, OLED, LED display segments).

• Relay control outputs.

• Voltage regulator outputs.

• Power-on indicator outputs.

• Current sense inputs/outputs.

• Power-up sequence testing.

• Power-down sequence testing.

• Voltage tolerance testing.

• Clock frequency and accuracy testing.

• Data integrity testing (checksum, CRC).

• Communication protocol testing (UART, SPI, I2C).

• Uploading Firmware or other files.

• Overvoltage protection testing.

• Undervoltage lockout testing.

• Logic functionality testing (gate-level/functional logic).

• Memory read/write testing (RAM, Flash).

• Sensor calibration and accuracy testing.

• ADC/DAC functionality and accuracy testing.

• Motor control functionality testing.

• Audio output quality testing.

• Display content and pixel testing.

• Communication protocol testing.

• Button/switch functionality testing.

• Temperature sensor accuracy testing.

All these I/O's and much more.