Is there any case law where a defendant's own testimony relating to his state of mind was excluded from his own testimony?

Fuentes argues that the district court erred in excluding portions of his own testimony relating to his state of mind, because this evidence was relevant and probative in negating the willfulness of his tax evasion. Willfulness is a necessary element of tax evasion under 26 U.S.C. 7201, which makes it a felony to "willfully attempt[ ] in any manner to evade or defeat any tax imposed" by federal law. In determining whether an evasion was willful, we look only to whether Fuentes had a good faith belief that the income was nontaxable, regardless of whether that belief was objectively reasonable. Cheek v. United States, 111 S.Ct. 604, 611 (1991).