Hydraulic Cement Mortars are typically formed by a combination of cement, sand, and water, but may include a variety of other materials in the mix. The strength of the final mortar is strongly dependent on the type of materials and the ratio of the components, and testing is required to determine the correct proportions for each application. ASTM C109 describes the methodology for testing the compression strength of mortars using cubes of material that are 2 inches on a side.
A mechanical testing machine equipped with the appropriate compression platens is used for the test. One of the platens must be spherically seated to allow slight tilt adjustment if the faces of the specimen are not perfectly parallel. The test machine operates in compression at slow test speeds in a load rate range indicated by the specification. Once the appropriate load rate is achieved a constant rate of movement is maintained through sample break. Accurate speed control is required in order to maintain the rate of motion once the sample begins to yield and ultimately break. Hydraulic compression testers are preferred for these tests due to their high force capacity. The results of the test may be recorded manually or electronically, depending on the system being used for the test.
A summary of ASTM C109 is given here. If you need to perform these tests please read the entire specification from the relevant ASTM publication.