An Oscilloscope could be used to monitor the test points and the output of systems or modules. A function generator injects the input or simulates a input condition. It could be Sine Wave, Triangle Wave, Ramp or Square wave. Frequency, Amplitude and Duty cycle (square) are variable settings.
For radios and amplifiers a simpler set is used it is called "Signal Injector" and "Signal Tracer". In Digital System a Pulse Generator and a Logic Probe may be used.
The AD5932 is a waveform generator providing a programmable frequency scan. Utilizing embedded digital processing allowing enhanced frequency control the device generates synthesized analog or digital frequency-stepped waveforms.
AD5932 - Programmable Single-Scan Waveform Generator
This product from Analog Devices is Active. Sinusoidal/triangular/square wave outputs. Output frequency up to 25 Mhz.
The chips below may not be in production, but available in some stores.
XR2206 - Monolithic Function Generator
The XR2206 is a monolithic function generator integrated circuit capable of producing high quality sine, square, triangle, ramp, and pulse waveforms of high-stability and accuracy. The output waveforms can be both amplitude and frequency modulated by an external voltage. Frequency of operation can be selected externally over a range of 0.01Hz to more than 1MHz.
XR2209 Voltage-Controlled Oscillator
The XR2209 is a monolithic voltage-controlled oscillator (VCO) integrated circuit featuring excellent frequency stability and a wide tuning range. The circuit provides simultaneous triangle and squarewave outputs over a frequency range of 0.01Hz to 1MHz. It is ideally suited for FM, FSK and sweep or tone generation, as well as for phase-locked loop applications. Waveform Generation Triangle, Sawtooth, Pulse, Squarewave.
ICL8038 Precision Waveform Generator/Voltage Controlled Oscillator
The ICL8038 waveform generator is a monolithic integrated circuit capable of producing high accuracy sine, square, triangular, sawtooth and pulse waveforms with a minimum of external components. The frequency (or repetition rate) can be selected externally from 0.001Hz to more than 300kHz using either resistors or capacitors, and frequency modulation and sweeping can be accomplished with an external voltage.
This was one of my favorite chips. This is of educational value. It was a pioneer chip a mixed cmos device. Make it a point to read the Datasheet. Chip may have been invented 1980 around. This is study material for college.
It is not available in stores. Some EE Engineer or Ham-DIY Enthusiast may have a few. Borrow and try it out for learning.
Science Fiction - Advanced Students can try configuring it in a Programmable Mixed Chip EDA tool plugin, if someone has developed that. Try taking a draft output on a semiconductor laser nano-milling prototype printer with a built in Mems pico-doper. If that works, lets go foundry!