#include <assert.h>
#include <stdio.h>
#include <math.h>
#include <setjmp.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int main(int argc, const char **argv) {
    char *val;

    assert(environ != NULL);
    assert(*environ == NULL);

    setenv("key1", "value1", 0);
    assert(environ != NULL);
    assert(!strcmp(*environ, "key1=value1"));
    assert(*(environ + 1) == NULL);

    setenv("key1", "value2", 0);
    assert(environ != NULL);
    assert(!strcmp(*environ, "key1=value1"));
    assert(*(environ + 1) == NULL);

    setenv("key1", "value3", 1);
    assert(environ != NULL);
    assert(!strcmp(*environ, "key1=value3"));
    assert(*(environ + 1) == NULL);

    setenv("key1", "longer-value", 1);
    assert(environ != NULL);
    assert(!strcmp(*environ, "key1=longer-value"));
    assert(*(environ + 1) == NULL);

    setenv("key2", "other-value", 0);
    assert(environ != NULL);
    assert(!strcmp(environ[0], "key1=longer-value"));
    assert(!strcmp(environ[1], "key2=other-value"));
    assert(environ[2] == NULL);

    assert(!strcmp(getenv("key1"), "longer-value"));
    assert(!strcmp(getenv("key2"), "other-value"));
    assert(getenv("key3") == NULL);

    unsetenv("key2");

    assert(!strcmp(getenv("key1"), "longer-value"));
    assert(getenv("key2") == NULL);
    assert(getenv("key3") == NULL);

    environ[0] = strdup("key2=???");

    assert(!strcmp(getenv("key2"), "???"));

    char *value = strdup("key4=!!!");
    putenv(value);

    assert(!strcmp(getenv("key2"), "???"));
    assert(!strcmp(getenv("key4"), "!!!"));

    value[6] = '@';

    assert(!strcmp(getenv("key2"), "???"));
    assert(!strcmp(getenv("key4"), "!@!"));

    unsetenv("key4");
    unsetenv("key2");

    assert(environ != NULL);
    assert(*environ == NULL);

    return 0;
}