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Decision table: A tool for analyzing and expressing situations where different operations are performed under multiple logical conditions.

Four elements:

(1) Conditional stake: list all the conditions of the problem;

(2) Action pile: list the possible actions of the problem specification;

(3) Condition items: list the values for the listed conditions;

(4) Action item: List the actions that should be taken under various values of the condition item.

Merger principles:

---Start with the same action item

---Same conditions are merged directly

---Opposite conditions ignored

Practical methods:

1. Determine the number of rules (assuming that there are n conditions, each condition has two values (0,1), so there are 2 n-th power rules);

2. List all condition piles and action piles;

3. Fill in the conditional items (such as 1 or 0);

4. Fill in the action item (Y);

5. Simplify and merge similar rules.

Advantages: It can list complex problems according to various possible situations, concise and easy to understand, and avoid omissions;

Disadvantages: Unable to express repeated actions, such as loop structures.

Causality diagram method: using graphical analysis of various combinations of inputs to obtain a judgment table.

Basic Symbols of Causality Diagram

The node on the left represents the cause and the node on the right represents the result. Meaning of identity, not, or, and:

Identity: if a=1, then b=1; if a=0, then b=0;

Not: if a=1, then b=0; if a=0, then b=1;

Or: if a=1 or b=1 or c=1, then d=1; if a= b= c=0, then d=0;

If a= b= c=1, then d=1; if a=0 or b=0 or c=0, then d=0.

When drawing a cause and effect diagram, the causes are on the left and the results are on the right, arranged from top to bottom, and connected by the above basic symbols according to the relationship between causes and results specified in the functional specification. Some intermediate nodes can also be introduced into the causal graph.

Some combinations of cause and cause, and cause and effect, are impossible because of grammatical or environmental constraints. In order to indicate these special cases, some symbols are used on the causal diagram to indicate constraints or constraints. The constraints of the causality diagram are shown in the figure below:

Mutex, inclusion, uniqueness and requirement are constraints on causes, and shielding is constraints on results. Their meanings are as follows:

Mutual exclusion E: indicates that there is no 1 at the same time, that is, there is only one 1 in a, b and c;

Contains I: indicates that there is at least one 1, i.e. a, b, c are not 0 at the same time;

Unique O: indicates that there is one and only one 1 in a, b and c;

Requirement R: If a=1, then b must be 1. It is impossible for a=1 and b=0.

Mask M: indicates that if a=1, then b must be 0

Using causality diagrams to derive test cases generally goes through the following steps:

1) Analyze what is the cause and what is the effect in the description of the software specification. The cause is the input or equivalence class of the input condition, and the result is the output condition. Assign an identifier to each cause and effect, and draw a cause-and-effect diagram from these relationships.

2) Some symbols are used on the causal diagram to indicate constraints or restrictions.

3) Analyze requirements and represent them as relationship diagrams between cause and effect diagrams.

4) Convert the causal diagram into a decision table.

5) Design test cases based on each column of the judgment table.

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