Here’s a comprehensive list of the main types of code coverage metrics used in software testing, ranging from basic to advanced:

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✅ 1. C0: Line Coverage (Statement Coverage)

• What it measures: Whether each line of code has been executed.
• Goal: Make sure all lines run at least once.
• Example: if is_valid(user): # Covered if condition is evaluated send_email(user) # Covered if executed

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✅ 2. C1: Branch Coverage (Decision Coverage / Condition Coverage)

• What it measures: Whether each decision (like if, else, case, loop conditions) has been evaluated both true and false.
• Goal: Ensure all branches of control structures are tested.

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✅ 3. C2: Path Coverage

• What it measures: Whether all possible execution paths through a function are executed.
• Goal: Ensure every unique route through the code is tested.
• Note: Path coverage grows exponentially with complexity, so it’s often impractical for large methods.

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✅ 4. Condition Coverage (or Predicate Coverage)

• What it measures: Whether each boolean sub-expression in a decision has been evaluated to both true and false.
• Example: if (A && B)
  • You must test:
    • A = true, B = false
    • A = false, B = true
    • A = true, B = true
    • A = false, B = false

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✅ 5. Modified Condition/Decision Coverage (MC/DC)

• What it measures: Whether each condition in a decision has been shown to independently affect the outcome of that decision.
• Used in: Aviation, automotive, medical systems (critical systems testing).
• Example:
  • For if (A && B), test cases must show that toggling A while keeping B fixed changes the decision result—and vice versa.

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✅ 6. Function Coverage

• What it measures: Whether each function or method is called during execution.
• Useful for: High-level view, especially in unit testing.

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✅ 7. Loop Coverage

• What it measures: Whether loops are executed:
  • Zero times (e.g. empty loop case)
  • One time
  • Multiple times
• Example: for i in range(n): print(i)
  • Test with n = 0, n = 1, and n > 1.

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✅ 8. Call Coverage

• What it measures: Whether function calls between modules/classes are exercised.
• Used for: Integration-level or system-level tests.

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✅ 9. Exception Coverage

• What it measures: Whether exception-handling code is covered (e.g. try, catch, finally blocks).
• Goal: Ensure error paths are tested.

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✅ 10. Data Flow Coverage

• What it measures: Tracks variables to see:
  • Where they’re defined (assigned),
  • Where they’re used (referenced),
  • And whether they’re used correctly.
• Types include:
  • Definition-use (DU) chains
  • All-defs, all-uses, all-paths

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✅ 11. Toggle Condition Coverage

• What it measures: Ensures that each condition’s change (toggle from true to false or vice versa) influences the outcome at least once.

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Summary Table

Metric	Focus Area	Practical Use
C0 (Line Coverage)	Statements	Basic test coverage
C1 (Branch Coverage)	Conditions/branches	Ensures if/else tested
C2 (Path Coverage)	Execution paths	Exhaustive, mostly theoretical
Condition Coverage	Boolean sub-conditions	Logic safety
MC/DC	Independence of conditions	Safety-critical industries
Function Coverage	Methods/functions	High-level view
Loop Coverage	Loop bodies	Loop logic correctness
Call Coverage	Inter-module function calls	Integration testing
Exception Coverage	Error-handling code	Robustness validation
Data Flow Coverage	Variable definition/use paths	Detects potential bugs or dead code

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Would you like a diagram or sample report showing how these look in real tools like SonarCloud, JaCoCo, or Istanbul?