They have to be testing for the metabolites of a benzo to find a benzo, for instance if they are using the standard test that doesn't include the expanded testing for benzo's a benzo is not going to show up as something else. If they were to look for Benzos they would have to use EMIT, TLC, or RIA Immunoassay, Immunoassays use antigen-antibody interactions to detect illegal substances. Antibodies that bind selectively to certain drugs or drug metabolites are chosen, and the sensitivity and the specificity of this test are only as good as the antibody chosen. The binding is proportional to the amount of drug in the urine and can be detected through enzymes, radioisotopes, or fluorescent compounds.
The RIA test is applied the same way as the EMIT. "The only difference btw RIA and EMIT is that RIA uses radioactive iodine as the detection mechanism rather than an enzyme NAD/NADH rxn which is detected by a scintillation counter" (anon1). The scintillation counter is used to measure the amount of radioactive particles present. Radioactivity is inversely proportional to metabolite level. RIA tests are a little more sensitive than the EMIT, and harder to beat. The most known user of the RIA test is the US government; in particular, the US military. The EMIT is more common because RIA produces radioactive waste, and radioactive waste is difficult to deal with. The US government uses RIA because a company gives the government the instrumentation free in exchange for buying their reagents. So you can see what a pain in the neck and imagine how much it costs for a employer to do the EMIT, TLC, or RIA Immunoassay. If the employer went all out and paid for the advanced full scale pre-screening tests, Benzodiazepines are only detectable by EMIT for 3-7 days. The absolute maximum detection period for Benzodiazepines is 42 days and to do that you need to involve Gas Chromatography / Mass Spectrometry or GC/MS is a two-step process, where GC separates the sample into its constituent parts, while MS provides the exact molecular identification of the compounds. Compounds are separated by GC and are then introduced, one at a time, into a mass spectrometer. As the sample constituents enter the MS, they are bombarded by electrons, which cause the compound to break up into molecular fragments. The fragmentation pattern is reproducible and characteristic, and is considered the "molecular-fingerprint" of a specific compound. Gas chromatography/mass spectrometry is considered to be the most definitive method for confirming the presence of a drug in the urine and is approximately 100 to 1,000 times more sensitive than TLC. Selective ion monitoring has been used to improve the GC/MS results. This procedure is the most costly, averaging approximately $200 per sample to test. so don't count on that for a common drug test. I've taken drug tests for many jobs (some with the Federal Gov.) and most places use a desktop computer with a thing that resembles a coffee machine called an "E-Screen". It probably cost very littlie and tests for the most basic of drugs, company's are not going to spend $200 to test every prospective employee. I took Valium / Diazepam every night last week and I feel confident taking a drug test today. In fact I am taking one today

I'm far more worried about the interview. PM me if you want I'll give you some recourses to look into about drug testing and drug tests. Good Luck!