RSpec expectations and matchers in Ruby - Step-by-Step Execution

Concept Flow - RSpec expectations and matchers

Start Test

↓

Set expectation

↓

Run code under test

↓

Compare actual vs expected

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Continue

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End Test

The test sets an expectation, runs code, compares actual and expected results, then passes or fails.

Execution Sample

Ruby

expect(5 + 3).to eq(8)
expect('ruby').to include('rub')
expect([1,2,3]).not_to be_empty

This code checks if 5+3 equals 8, if 'ruby' includes 'rub', and if the array is not empty.

Execution Table

Step	Expectation	Actual Value	Matcher	Result	Pass/Fail
1	expect(5 + 3).to eq(8)	8	eq(8)	8 == 8	Pass
2	expect('ruby').to include('rub')	'ruby'	include('rub')	'ruby' includes 'rub'	Pass
3	expect([1,2,3]).not_to be_empty	[1,2,3]	not_to be_empty	Array is not empty	Pass

💡 All expectations passed, test completes successfully.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
actual_value	nil	8	'ruby'	[1,2,3]	[1,2,3]
expectation_result	nil	Pass	Pass	Pass	Pass

Key Moments - 2 Insights

Why does expect(5 + 3).to eq(8) pass even though 5 + 3 is an expression?

The expression 5 + 3 is evaluated first to 8, then compared to 8 using eq matcher, so it passes as shown in execution_table step 1.

What does 'not_to be_empty' mean in the third expectation?

'not_to be_empty' checks that the array is NOT empty. Since [1,2,3] has elements, it passes as shown in step 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the actual value checked in step 2?

A 8

B 'ruby'

C 'rub'

D [1,2,3]

💡 Hint

Check the 'Actual Value' column in execution_table row 2.

At which step does the matcher check that the array is not empty?

A Step 1

B Step 2

C Step 3

D None

💡 Hint

Look at the 'Matcher' column in execution_table for step 3.

If expect(5 + 3).to eq(9) was used instead, what would happen in the execution table?

A Step 1 would show Fail

B Step 1 would show Pass

C Step 2 would show Fail

D No change

💡 Hint

Compare actual value 8 with expected 9 in step 1's 'Result' column.

Concept Snapshot

RSpec expectations check if code results match what we want.
Use expect(actual).to matcher(expected) for positive checks.
Use expect(actual).not_to matcher for negative checks.
Common matchers: eq, include, be_empty.
Tests pass if actual matches expected, else fail.

Full Transcript

RSpec expectations and matchers let us write tests that check if code behaves as expected. We write expect statements with actual values and matchers to compare them. For example, expect(5 + 3).to eq(8) checks if 5 plus 3 equals 8. The test runs the code, compares actual and expected, and passes or fails accordingly. Matchers like eq check equality, include checks if a string contains a substring, and be_empty checks if a collection is empty. Using not_to reverses the check. The execution table shows each step's actual value, matcher used, and result. This helps beginners see how tests run step-by-step.