Function generator to test filter capacitors
It really depends on the value that your trying to measure and to what accuracy you are trying to measure it. Realize that you are going to have noise in your system and probably the biggest limiting factor will be the resolution of your scope. Buy the function generator with a range based on the desired frequency below.

Here is a great article on how to measure capacitance or inductance. In short you are measuring the reluctance of the circuit. 

If you know some algebra and want to use this method for capacitors instead of indicators it works well. You pick a point say 1/2 of your input voltage and then solve the equations for that. I usually do a sweep and then fit the entire equation to a curve so I have multiple points that average but only one point should suffice. 
$$ \left|\frac{Vscope}{Vgen} \right|= \left|\frac{\frac{j\omega}{C}}{R+\frac{j\omega}{C}} \right| = \left|\frac{\omega^2}{(RC)^2+\omega^2} +j\frac{RC\omega}{(RC)^2+\omega^2} \right| = ...= \frac{\omega
}{\sqrt{(CR)^2+\omega^2}}$$

And then solving for \$ \omega\$ which is \$ 2\pi f \$ with R = 50

$$ \frac{1}{2}=\frac{\omega
}{\sqrt{(CR)^2+\omega^2}} \Rightarrow C=\frac{\omega\sqrt{3}
}{R} $$

Here is the circuit for reference







simulate this circuit &ndash; Schematic created using CircuitLab