Marble Testing

Marble Testing

• Marble testing provide a simple way to describe observable streams.
• They can be used to model and test observables.
• They can also be used to model and test subscriptions.
• Uses a scheduler to provide timing.
• Timing is done frame-by-frame.
• Each character in a marble is 10 frames​. A frame is a virtual "millisecond" or "clock cycle" of the scheduler.

Marble Diagram

Review a marble diagram:

Syntax

• The first character is "zero frame".
• A dash "-" represents the passage of 10 frames.
• A pipe "|" indicates completion notification.
• A hash "#" indicates error notification.
• A carrot "^" indicates subscription point in a hot observable.
• Any other character indicates next notification.

Examples

Emit a value and complete:

cold('--a--|');

• Two dashes "-" represents the passage of 20 frames.
• The letter "a" represents our first emitted value.
• A pipe "|" represents completion.
• The mocked cold observable is a total of 60 frames.

Emit a value and error:

cold('--a--#');

• Two dashes "-" represent the passage of 20 frames.
• The letter "a" represents our first emitted value.
• A pipe "#" represents an error.
• The mocked cold observable is 60 frames.

Emit multiple values and complete:

cold('--a-b--|');

• The letter "a" represents our first emitted value.
• The letter "b" represents our second emitted value.
• The observable is 80 frames.

Cold vs Hot

• A cold observable does not produce values until there is at least one subscriber until complete or all subscribers have unsubscribed.
• A hot observable produces values regardless of the subscribers.