papers/lux-distributed-systems-testing/sections/02-layer-1-unit-tests.tex

\section{Layer 1: Unit Tests}


\subsection{What to Test}

Unit tests verify individual functions in isolation. For a blockchain node:

\begin{itemize}[nosep]
  \item Serialization/deserialization of messages, blocks, transactions.
  \item Cryptographic operations (signature, hash, verification).
  \item State transition logic (apply block to state).
  \item Data structure operations (merkle tree insert/proof/verify).
  \item Validator set management (add, remove, weight calculation).
\end{itemize}

\subsection{Go Test Patterns}

\begin{lstlisting}[language=Go,caption={Table-driven unit test}]
func TestBlockValidation(t *testing.T) {
    tests := []struct {
        name    string
        block   Block
        wantErr error
    }{
        {
            name:    "valid block",
            block:   validBlock(),
            wantErr: nil,
        },
        {
            name:    "empty parent hash",
            block:   blockWithEmptyParent(),
            wantErr: ErrInvalidParentHash,
        },
        {
            name:    "timestamp in future",
            block:   blockWithFutureTimestamp(),
            wantErr: ErrFutureBlock,
        },
        {
            name:    "insufficient signatures",
            block:   blockWithTooFewSigs(),
            wantErr: ErrInsufficientQuorum,
        },
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            err := ValidateBlock(tt.block)
            if !errors.Is(err, tt.wantErr) {
                t.Errorf("ValidateBlock() = %v, want %v",
                    err, tt.wantErr)
            }
        })
    }
}
\end{lstlisting}

\subsection{Coverage Requirements}

We require 80\% line coverage for the node codebase. More importantly, we require 100\%
coverage of error paths: every \texttt{if err != nil} branch must be exercised by a test
that triggers that error.

\begin{lstlisting}[language=bash,caption={Running Go tests with coverage}]
go test -v -race -coverprofile=coverage.out ./...
go tool cover -func=coverage.out | grep total
# total:  (statements)  83.2%
\end{lstlisting}

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