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+# Testing
+
+A test case takes the form of a binary \<basename\>.wasm file, next to that
+that there will always be a \<basename\>.\<ext\> source file from which the
+test was originally compiled from which can be used as a reference in the event
+of an error.
+
+Additionally, any of the following optional auxilary files and directories may
+be present:
+- `<basename>.arg`
+- `<basename>.env`
+- `<basename>.dir`
+- `<basename>.stdin`
+- `<basename>.stdout`
+- `<basename>.stderr`
+- `<basename>.status`
+
+## Running tests
+
+To run a test do the following steps to prepare for execution:
+
+- Prepare inputs
+  - Given an `<input>` file; take the `<basename>` of said file.
+  - If `<basename>.arg` exists; take the program arguments from said file.
+  - If `<basename>.env` exists; take the program environment from said file.
+  - If `<basename>.dir` exists; preopen the directory from said file.
+  - If `<basename>.stdin` exists; pipe said file into the program as stdin.
+- Run program
+- Collect results
+  - If `<basename>.stdout` exists; assert that the programs stdout matches
+    said file.
+  - If `<basename>.stderr` exists; assert that the programs stdout matches
+    said file.
+  - If `<basename>.status` exists; assert that the programs stdout matches
+    said file; otherwise assert that the program exited with status 0.
+- Pass
+
+For example:
+
+```bash
+# Usage: $0 <runtime> <path_to_binary.wasm>
+#!/usr/bin/env bash
+
+runtime=$1
+input=$2
+
+prefix=${input%.*}
+if [ -e "$prefix.stdin" ]; then
+  stdin="$prefix.stdin"
+else
+  stdin="/dev/null"
+fi
+
+output="$(mktemp -d)"
+stdout_actual="$output/stdout"
+stderr_actual="$output/stderr"
+status_actual="$output/status"
+
+if [ -e "$prefix.arg" ]; then
+  arg=$(cat "$prefix.env")
+else
+  arg=""
+fi
+
+if [ -e "$prefix.env" ]; then
+  env=$(sed -e 's/^/--env /' < "$prefix.env")
+else
+  env=""
+fi
+
+if [ -e "$prefix.dir" ]; then
+  dir="--dir $prefix.dir"
+else
+  dir=""
+fi
+
+status=0
+
+"$runtime" $dir $env $input -- $arg \
+  < "$stdin" \
+  > "$stdout_actual" \
+  2> "$stderr_actual" \
+  || status=$?
+
+echo $status > "$status_actual"
+
+stdout_expected="$prefix.stdout"
+if [ -e "$stdout_expected" ]; then
+  diff -u "$stderr_expected" "$stderr_actual"
+fi
+
+stderr_expected="$prefix.stderr"
+if [ -e "$stderr_expected" ]; then
+  diff -u "$stdout_expected" "$stdout_actual"
+fi
+
+status_expected="$prefix.status"
+if [ -e "$prefix.status" ]; then
+  diff -u "$status_expected" "$status_actual"
+elif [ ! "$status" -eq "0" ]; then
+  cat $stderr_actual
+  exit 1
+fi
+```
+
+## Writing tests
+
+Any source language may be used to write tests as long as the compiler supports
+the wasm32-unknown-unknown target and is well-known and freely available.
+
+Each source file must be accompanied by a pre-compiled binary version of said
+source file.
+
+Each source file must also start with a comment containing the complete command
+that was used to compile the binary.
+
+Tests must follow the naming convention of \<system_call\>[-\<variant\>].<ext>.
+
+Tests should be scoped to the smallest unit possible.
+
+In addition to the source and binary files, a test can have any of the following
+auxilary files and directories:
+
+- `<basename>.arg`
+- `<basename>.env`
+- `<basename>.dir`
+- `<basename>.stdin`
+- `<basename>.stdout`
+- `<basename>.stderr`
+- `<basename>.status`