Universal Turning Point and Inflection Point Tests R package tptest version 1.0.3 Performs turning point and inflection point tests for U-shaped and inverse U-shaped relationships in regression models. Implements the Sasabuchi (1980) test as extended by Lind and Mehlum (2010) with support for quadratic, cubic, log-quadratic, and inverse functional forms. Features include delta-method standard errors, Fieller confidence intervals, Simonsohn (2018) two-lines test, and parametric bootstrap. Designed for post-estimation analysis of linear models, panel models, and quantile regression. References: Lind and Mehlum (2010) <doi:10.1111/j.1468-0084.2009.00569.x>; Sasabuchi (1980); Fieller (1954) <doi:10.1111/j.2517-6161.1954.tb00159.x>. Software Depends: R (>= 4.0.0) Imports: stats, graphics Suggests: testthat (>= 3.0.0), knitr, rmarkdown, lmtest, sandwich, plm, quantreg Muhammad Alkhalaf <muhammedalkhalaf@gmail.com> Comprehensive R Archive Network (CRAN) Muhammad Alkhalaf [aut, cre, cph] (ORCID: <https://orcid.org/0009-0002-2677-9246>) GPL-3 2026-04-09 application/tgz https://CRAN.R-project.org/package=tptest doi:10.32614/CRAN.package.tptest