Terminology

Decisions, Conditions & Branches

flowchart TD
  %% Nodes
  Entry(("IN"))
  OutT(("OUT True"))
  OutF(("OUT False"))
  Note["<b>Conditions:</b><br>Logical Operators<br>(AND/OR)"]

  %% Subgraph for a Basic Block
  subgraph BB["Basic Block"]
    direction TB
    STMS["a = a + 1;<br>b[i] = c + 5;<br>…<br>char last = argstr.CharAt(0);"]
    DEC{"Decision:<br>a > b && c == 1"}
  end

  %% Control Flow
  Entry --> BB
  %% BB --> STMS
  STMS --> DEC
  DEC -->|True| OutT
  DEC -->|False| OutF

  %% Simulated Note
  Note -.-> DEC

  %% Styling
  style STMS fill:#e0f0ff,stroke:#0077cc
  style DEC  fill:#ffd0d0,stroke:#cc0000,stroke-width:2px
  style Note fill:#ffffcc,stroke:#999,stroke-dasharray: 5 5,font-size:12px

Reference: Adapted from A. Hass, Guide to Advanced Software Testing, 2008 [1]

1. Statement

   • The smallest executable unit in code (non-comment, non-whitespace).
   • Example: x = y + 1 or return z;.

2. Basic Block

   • A sequence of one or more statements that always execute together.
   • Entry at the first statement; exit at the last.
   • No internal branches—only the last statement can transfer control elsewhere.

3. Decision (Branch Point)

   • A statement whose outcome (True/False or multiple cases) determines the next basic block.

   • Examples:

     • IF … THEN … ELSE
     • FOR …, WHILE …, DO … WHILE
     • CASE … OF

4. Branch

   • A directed edge in the control-flow graph representing one possible outcome of a decision.
   • Each decision can have two or more branches (e.g., True/False or multiple CASE labels).

5. Condition

   • A Boolean expression evaluated inside a decision (e.g., A > B).
   • Decisions may combine several conditions with logical operators (&&, ||).

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Control-Flow Graphs (CFG)

A control-flow graph models all possible execution paths through a program:

• Nodes

  • Represent either individual statements or basic blocks.

• Edges

  • Represent possible transfers of control (which statement/block follows).

Key properties:

• There is a unique start node and end node.
• Nodes with multiple outgoing edges are decision points.
• An execution path is any sequence of nodes and edges from start to end (or between any two nodes).

Why CFGs matter:

• They provide the foundation for structural testing (statement, branch, path coverage).
• They help identify all decision points and possible execution paths.

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Compact CFG via Basic Blocks

Instead of one node per statement, we can merge consecutive non-branching statements into a basic-block node:

1. Partition the code into basic blocks.
2. Build a graph where each node is a block, and edges represent jumps between blocks.
3. This yields a smaller but equivalent CFG for analysis and coverage metrics.

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Example: Simple IF/ELSE CFG

The example below demonstrates a CFG with two decision nodes.

The figure shows a Test case: A=true, B=false

The execution path for this test case is shown in red on the diagram.

The set of all selected test cases is a Test suite. For example, Test suite = Test case 1: A=true, B=false + Test case 1: A=true, B=true

flowchart TD
    %% Define start and end as circles
    Start((Start))
    End((End))

    %% Decision nodes as diamonds
    A{Condition: A?}
    D{Condition: B?}

    %% Action blocks
    B[Block S1]
    C[Block S2]
    E[Block S3]
    F[Block S4]

    %% Control flow
    Start --> A
    A -->|True| B
    A -->|False| C
    B --> D
    C --> D
    D -->|True| E
    D -->|False| F
    E --> End
    F --> End

    %% Highlighted execution path: A=true, B=false
    linkStyle 0 stroke:#ff0000,stroke-width:3px
    linkStyle 1 stroke:#ff0000,stroke-width:3px
    linkStyle 3 stroke:#ff0000,stroke-width:3px
    linkStyle 6 stroke:#ff0000,stroke-width:3px
    linkStyle 8 stroke:#ff0000,stroke-width:3px

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For data-flow coverage criteria (Definition-Use pairs, All-Defs, All-Uses, All-DU-Paths), see Data Flow Coverage.

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References

1. A. M. Hass, Guide to advanced software testing. Artech House, 2014.

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