When an @NgModule is imported more than once in the testing module (for
example it appears in the imports of more than one module, or if it's
literally listed multiple times), then TestBed had a bug where the
providers for the module would be overridden many times.
This alone was problematic but would not break tests. However, the original
value of the providers field of the ngInjectorDef was saved each time, and
restored in the same order. Thus, if the provider array was [X], and
overrides were applied twice, then the override array would become
[X, X'] and then [X, X', X, X']. However, on the second override the state
[X, X'] would be stored as original. The array would then be restored to
[X] and then [X, X'].
Each test, therefore, would continue to double the size of the providers
array for the module, eventually exhausting the browser's memory.
This commit adds a Set to track when overrides have been applied to a module
and refrain from applying them more than once.
PR Close#29571
7b27009e20