change
It just verifies that the state has changed. I don't care about "what changed to what" or "how changed".
If you add 1 to x, change holds.
x = 1 expect { x += 1 }.to change { x } # => true
Even if 2 is added to x, change holds.
x = 1 expect { x += 2 }.to change { x } # => true
Add 1 to x and subtract 1 more. Since the state has not changed, change does not hold.
x = 1 expect { x += 1; x -= 1; }.to change { x } # => RSpec::Expectations::ExpectationNotMetError: result should have changed, but is still 1
change.by
Verify the increase or decrease of the value with the relative value.
If the value is increased by 5, change.by(5) holds.
x = 1 expect { x += 5 }.to change { x }.by(5) # => true
If the value decreases by 5, change.by(-5) holds.
x = 1 expect { x -= 5 }.to change { x }.by(-5) # => true
As we do not verify "absolute value" after increase and decrease, we are careful. For example, when calculating 3 + 4, change.by(7) does not hold.
x = 3 expect { x += 4 }.to change { x }.by(7) # => RSpec::Expectations::ExpectationNotMetError: result should have been changed by 7, but was changed by 4
The increased value is 4, so it is change.by(4) that holds.
x = 3 expect { x += 4 }.to change { x }.by(4) # => true
change.from.to
Verify what has changed from what state. For example, if you calculate x = 3 + 4 , the value changes from 3 to 7.
Therefore, change.from(3).to(7) holds.
x = 3 expect { x += 4 }.to change { x }.from(3).to(7) # => true
Original by
RSpec - change の基本動作。 ( by / from / to の使い方 )
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