What is the test for essential and indispensable steps in the process of imposing or levying a tax?

It argues, in reliance on the statement of Strong J. in O’Brien v. Cogswell (1890), 1889 CanLII 67 (SCC), 17 S.C.R. 420 at para. 3, that all steps prescribed by a taxing statute in the process of imposing or levying a tax must be considered essential and indispensable unless the statute otherwise provides: The general principles applicable to the construction of statutes imposing and regulating the enforcement of taxes for general and municipal purposes are well settled. … all steps prescribed by the statute to be taken in the process either of imposing or levying the tax are to be considered essential and indispensable unless the statute expressly provides that their omission shall not be fatal to the legal validity of the proceedings; in other words, the provisions requiring notices to be given and other formalities to be observed are to be construed as imperative, and not as merely directory, unless the contrary is explicitly declared.