I had the same error when I updated Angular to version >= 9 (Token InjectionToken XxXxXxXx is missing a ɵprov definition), especifically when I ran tests and these tests had providers as MatDialogRef and MAT_DIALOG_DATA from Angular Material.
My solution was replace the providers config in the beforeEach() section. look at:
Before:
import { MatDialogRef, MAT_DIALOG_DATA } from '@angular/material/dialog';
beforeEach(async(() => {
            TestBed.configureTestingModule({
                    imports : [
                        ...
                    ],
                    declarations: [
                        ...
                    ],
                    providers: [
                        { provide: MatDialogRef },
                        { provide: MAT_DIALOG_DATA }
                    ]
            }).compileComponents();
    })); 
After:
import { MAT_DIALOG_DEFAULT_OPTIONS } from '@angular/material/dialog';
beforeEach(async(() => {
            TestBed.configureTestingModule({
                    imports : [
                        ...
                    ],
                    declarations: [
                        ...
                    ],
                    providers: [{
                        provide: MAT_DIALOG_DEFAULT_OPTIONS, useValue: {hasBackdrop: false}
                    }]
            }).compileComponents();