The aim of this paper is to present a theoretical and empirical overview of the hypothesis that patients’ behavior in psychotherapy can be understood as an expression of their efforts to disprove their pathogenic beliefs by testing them in the therapeutic relationship. According to Control–Mastery Theory (CMT; Gazzillo, 2016; Silberschatz, 2005; Weiss, 1986, 1994), psychopathology stems from unconscious pathogenic beliefs developed in response to early traumas. Pathogenic beliefs associate the achievement of healthy goals with a variety of unconsciously perceived dangers. Thanks to the inborn human motivation to adapt to reality and to the power of adaptive unconscious mental functioning, patients come to therapy with a unconscious plan to overcome their pathogenic beliefs by testing them with their therapists. Tests are consciously or unconsciously devised actions aimed at disproving pathogenic beliefs. CMT describes two broad categories of tests: transference tests and passive-into-active tests. Tests require specific responses from the therapist to be passed. When therapists pass patients’ tests, patients feel safer and may make therapeutic progress; when tests are failed, patients feel endangered and may get worse. Consistent with CMT assumptions, studies on testing have shown that a therapist passing a patient’s tests is associated with immediate positive effects on the patient, but more studies are needed.