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Assertions are errors that may occur on a MongoDB server from time to time. Administrators need to promptly capture these errors and understand their nature, so that they can rapidly resolve them and prevent any negative impact on database performance. This is where the MongoAssertsTest test helps. This test captures and reports the rate at which each type of assertion occurs on a monitored MongoDB server. Using these metrics, administrators can instantly capture the asserts/errors, quickly determine from the assert type why the error might have occurred, and then, rapidly initiate the appropriate corrective measures.

Outputs of the test : One set of results for the target Mongo database server being monitored.

Measurement	Description	Measurement Unit	Interpretation
Regular_assert_rate	Defines the rate at which regular asserts occurred on the monitored MongoDB server.	Asserts/Sec	Regular asserts are per-operation variants (eg., “unexpected failure while reading a BSON document”). Ideally, the value of this measure should be 0. If a non-zero value is reported, check the log file for more information.
Warning_assert_rate	Indicates the rate at which warning asserts occurred on the monitored MongoDB server.	Asserts/Sec	Warning asserts are not as serious as errors. They just indicate conditions that might be worth checking like too low ulimit or readahead. Ideally, the value of this measure should be 0. If a non-zero value is reported, check the log file for more information.
Message_assert_rate	Indicates the rate at which message asserts occurred on the monitored MongoDB server.	Asserts/Sec	Message asserts indicate internal server exceptions. Ideally, the value of this measure should be 0. If a non-zero value is reported, check the log file for more information.
User_assert_rate	Indicates the rate at which user asserts occurred on the monitored MongoDB server.	Asserts/Sec	User asserts are triggered as the result of user operations or commands generating an error like a full disk space, a duplicate key exception, or write errors (e.g. insert not properly formatted, or no access right). These errors are returned to the client so most of them won't be logged into the mongod logs. However you should investigate potential problems with your application or deployment. Both regular and user asserts will result in the corresponding operation failing.