How do I verify a method was called exactly once with Moq?

You can use Times.Once(), or Times.Exactly(1):

mockContext.Verify(x => x.SaveChanges(), Times.Once());
mockContext.Verify(x => x.SaveChanges(), Times.Exactly(1));

Here are the methods on the Times class:

• AtLeast – Specifies that a mocked method should be invoked times times as minimum.
• AtLeastOnce – Specifies that a mocked method should be invoked one time as minimum.
• AtMost – Specifies that a mocked method should be invoked times time as maximum.
• AtMostOnce – Specifies that a mocked method should be invoked one time as maximum.
• Between – Specifies that a mocked method should be invoked between from and to times.
• Exactly – Specifies that a mocked method should be invoked exactly times times.
• Never – Specifies that a mocked method should not be invoked.
• Once – Specifies that a mocked method should be invoked exactly one time.

Just remember that they are method calls; I kept getting tripped up, thinking they were properties and forgetting the parentheses.