The code uses an operator for comparison when the intention was to perform an assignment.
In many languages, the compare statement is very close in appearance to the assignment statement; they are often confused.
Many IDEs and static analysis products will detect this problem.
The assignment will not take place, which should cause obvious program execution problems.
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)