DOT Drug and Alcohol Tests include:
Pre-employment – An employer must receive a negative drug test result before permitting a CDL driver to operate a CMV. 
Post-accident – Drug and alcohol tests may be required after crashes. Any time the accident results in a fatality.
Any time the accident results in a fatality; If the commercial driver receives a citation AND someone in the accident is injured and receives immediate medical attention away from the scene; or If the commercial driver receives a citation AND one or more vehicles incur disabling damage requiring the vehicle to be towed from the scene. If the accident only involves getting on or off the vehicle, or the loading or unloading of cargo, the driver would not be required to have a post-accident drug or alcohol test.
Pre-Employment
New drivers must be drug tested with a negative result before an employer can permit them to operate a CMV on a public road. Alcohol testing is permitted only if it applies to all CDL drivers. If a driver is removed from a random testing pool for more than 30 days, the driver must again be pre-employment tested.
Post-Accident
CDL drivers must be drug and alcohol tested whenever they are involved in a fatal accident, or receive a traffic citation resulting from an injury or vehicle-disabling accident. The alcohol test must occur within 8 hours, and the drug test must occur within 32 hours.

Random-Testing
Random tests MUST be unannounced. A driver may be directed to take a drug test even when at home in an off-duty status. Random alcohol testing may only occur when the driver is on-duty or immediately before or after. Once notified to report for random testing, the driver must immediately report to the testing location. A delayed arrival may be considered a refusal which is equivalent to testing positive.
Reasonable Suspicion
Drivers who appear to be under the influence of drugs or alcohol can be immediately tested (§382.307). Employers must train CDL driver supervisors to detect the symptoms of driver impairment (§382.603).
Return-to-Duty (RTD)
Required for drivers who tested positive, refused, or otherwise violated the prohibitions of 49 CFR Part 382 Subpart B; and who have completed the return-to-duty process with a DOT-qualified substance abuse professional. This test is directly observed, and a negative result is required before resuming driving duties (§382.309 and §40.305).
Follow-Up
Required for drivers who tested positive, refused, or otherwise violated the prohibitions of 49 CFR Part 382 Subpart B; and who have completed the return-to-duty process with a DOT-qualified substance abuse professional, and have tested negative for a return-to-duty test. This testing is prescribed by the substance abuse professional for a minimum of 6 directly observed tests in 12 months, but can be extended an additional four years (§382.311 and §40.307).