how can I test a diode for opened or shorted circuit?

A diode is not a passive part. It requires a voltage often about 0.7 volts to operate. It acts like a check valve. When less voltage than that is going through it, it will be open and not allow any backflow of current. When the voltage threshold is reached it will then short and allow current to pass through it.

Some mulitmeters have a diode testing function which will apply that small voltage and check for continuity that is probably your best bet to see if it is working. Otherwise some more intensive electronic equipment is needed to test it.

Be careful of polarity of the leads from the ohmeter to the diode. You will get very different readings if you swap the two leads and change the polarity. It's entirely possible to read 5 ohms in one direction and 90 k in the other.

So until you do that, I can't tell which is good and which is bad.

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A simple test with an multimeter set to read resistance will tell you. You do NOT need a diode tester as the meter MUST provide current to test resistance to begin with. Check continuity and then reverse the leads. You should have extremely high readings in one direction, low readings in the other.If you get low readings in both directions, the diode is shorted, if high readings in both directions, the diode is open.

Before do this test,one lead of diode under test must remove away from the circuit.

[1] With a digital meter, set it into diode test, apply RED probe to anode of diode,Black probe to other cathode. It should read 0.5 to 0.6 volt for most silicon diode. 0.2 volts for Ge diode. Zener diode needs to be tested with other way. Never use digital ohm-meter to measure diode. It gives confusion result.

OR

[2] With an analogy ohm meter that has 1.5 v or 3v built-in test source. Never set to high ohm range because some ohm meter has 9v or 15v or 30v built-in test source that might damage the diode being tested under forward bias.Apply ohm-meter + probe to anode of diode, - probe to cathode.
For most Si diode,it shows below 1000 ohm BUT NEVER READ CLOSE TO ZERO OHM.
Now reverse both probes and do the same test,it shows almost infinite resistance. If you see a small reading like 1M ohm or less. This is a bad leakage diode.

For OPEN diode,test result shows both infinite resistance.
For SHORT diode, test result shows both close to ZERO ohm.

To test Ge signal diode,do the same test. But the test result for reverse bias, any reading more than 100k ohm is considered GOOD.